Google Python Class Day 1 Part 3

>>PARLANTE: All right, hey, everybody. All
right [INDISTINCT] a lot of people working away on this one. It’s our requirement that
you finish like all the problems on this one, I’m just hoping that if you could get like,
some of them. What I’d like to do, is I want to do another quick lecture section then I
want to break our time for, you know, the nice long exercise at the end. And you’re
welcome to keep working on the list problems if you want, but this last exercise, once
we have file reading, then could begin to look like a real program. And it’s going to
involve–it’s going to sum up all the material we’ve talked about, lists and strings also,
put it all together and that’ll be the last thing for today. So, the last day I was sure
to show you is the HashTable or also called the dictionary. It’s a very useful data structure,
it’s built-in to Python; it’s pretty easy to use. So, the delimiter character for a
dictionary is the curly brace. So here, I’ll create one. I’ll say D is equal to left curly
brace, right curly brace. I’ll just create an empty one. And the way the dictionary works–and
I’ve got a little piece of art there from the hand out at the top–is you can think
of it as a–it’s said to contain key value bindings. For each key, it can look up that
value very quickly. So, the way that works in Python is I’ll say, under the key A, I
would like to store the string alpha, and under the string O–I’m just going to make
the same example I have in that little picture there–I’ll store omega, and under the key
G, I’ll store gamma, put it there on my [INDISTINCT]. So, what HashTable does is you always talk
to it in terms of keys. You say, “Dictionary, please store this key,” and it will store
whatever. And then later on, when you try and retrieve by key–this is the one thing
that HashTables are fast at–it can retrieve via key in constant time. It’s just as fast
as you can imagine, it’s very quick at key retrieval. So, for example, if I say, okay
dictionary–and I–in Python, the way it works is we just use the square brackets. When I
use the square bracket on the left, I was storing a value in. So, that series of three
assignments, that builds exactly this picture of the dictionary. So, you can think of the
dictionary as what has a set of keys and each–for each key it points to some value. If I want
to look–do a look up, I would say, well instead of–just don’t put it on the left hand side
of an equal. So, if I just say D of A, it just returns the value, oh alpha. Now, not
to belay with the point too much, that’s the one thing that dictionaries are fast at. You
could put 10 million keys in this dictionary, and yet for a particular one, you could call
it up and it would call it up in just a few cycles on the machine. It’s very, very fast
at key look up, that’s the one thing that it does. So, let me show you, you know, a
few more features you could do with dictionaries. So, obviously, you can store stuff in, you
could use the square right to get stuff out. If I refer to a key that is not in there,
I say, “All right dictionary, what do you have for key value X?” What I get is actually
an error, a key error so that’s a–it’s a long puzzle. I think Python is trying to be
sort of consistent with the list here, that if I said list, square bracket like a thousand
and there is no thousand–you know, it would’ve given an error. So, I think there’s sort of
an attempt to be kind of consistent with what square bracket means. And square bracket means,
yeah, it should’ve been there and if you refer to something that’s not there, it’s an error.
Fortunately, there’s an alternative if you use–there’s a dot get method on the dictionary.
And so, if you do dot get, in the simplest form, what it does is it returns the value
none, if it’s not in there and otherwise returns the value. So, if I say dot get of A, then
I get alpha, but of X then I just get back nothing. It happens in the interpreter, none
is sort of a special case, it just prints nothing; it just comes back. So, if you want
to distinguish, you know if you want–if you care where the nothing is in there, then you
could use get and you’re more protected. How do you suppose you test if a value is in a
dictionary, someone say? Something I wrote I think over there, yeah, all right. While
waiting for his in, right? Dictionary is just another composite thing just like a list.
So, I can just say A in the dictionary it’s like yup, it is. Like, all right, I could
say, was x in there? No, it’s not. So, can you kind of live, live a little higher on
the food chain, use those built-ins. So, I’m going to–well here, I’ll show you some more
features first. So, the dictionary as itself is–it’s just good at this sort of key value
storage, that’s all it does. One thing that’s kind of common is you open a file and you
read a bunch of data; you store it all on a dictionary to kind of organize it. And then,
once you’re done with it, you want to loop over the dictionary and kind of look at all
the contents. So, the simplest way to do that is the dictionary has a method called dot
keys and what does is it returns a list of just the keys. There’s also a list of–oh,
and notice the keys are in kind of random order. Now, in this case I guess they appear
to be in alphabetical order, but as the dictionary gets bigger and bigger, these will be in kind
of a random order. This is the hashing strategy that the dictionary uses causes the keys to
be in a scrambled order. I’m sure I’m probably switching between the word dictionary and
the word HashTable, so better yet those are for the same thing. And hashing is this general
strategy that’s very powerful, you’ll see it just crop up in a lot of languages. So,
the–likewise, there is a dot values, oops what’s the problem there? I spelled it wrong.
So, this just pulls out the linear list of values. So, it’s actually, it’s in a kind
of a random order, but it’s in the same random order that the dot keys was. So, I’m going
to show you what I would regard as kind of the most common case of looping over a dictionary.
You’ve built the dictionary, it’s got all this, you know, social security numbers or
URLs or whatever in it and now you want to loop over and look at them. I would write
it this way, I’d say, “Well, for K in dictionary dot keys.” All right, so, what that means
is go to the dictionary, pull out the linear list of keys and now, I want to loop over
that. But, it’s just sort of as a nicety; the keys are going to come out in kind of
random order. So, let’s loop over the sorted of that. Pull out the keys, sort them, now
loop over them and write this all on my mind, I’m going to say like, well what I could print
is–I mean, let’s say I want to print a little thing with like an arrow, like this key goes
to this value. I could say print. First of all, the dictionary, square bracket K so just–that’s
the–I’m sorry, don’t do it (ph). I’ll do it, I’ll say key colon, comma K, and I’ll
say comma, and I’ll draw like a little arrow and I’ll say dictionary square bracket K.
So, if I run that without so many errors, so that’s going to pull out the keys, it’s
going to loop through all the keys. And then, for each one, it’s doing this little line
up like, here’s what the key is and here is what–here is the value that is stored for
that key. So, that is the most–I think dot keys and dot values are the most common case.
There is this one other case which is called dot items. And what dot items does isn’t–rather
than just pulling out the key or just pulling out the value, it pulls them both out simultaneously
and it puts each one in a tuple-sized two. So, what you’re seeing here is a list of tuples.
Each tuple is length two and each tuple represents one–what I would call a binding from the
dictionary. And so, what you could do is you could–if you really want to just get the
key value all in one step, then you could use dot items. So, for example, I could say
for tuple in d dot items colon, you know, print the tuple or whatever. All right, check
it out, I left off the prints. So, that’s another way of kind of dealing with all of
the data of the dictionary, you know, once you’ve built it up. You know, okay, I think
that’s–I’m not going to show you the other thing, it seems messy enough. So, now I’m
going to sort of step outside for saying–I mean, what is the dictionary good for? Suppose
you’ve got an Apache log file of like, 20 million get requests and in a sense, the Apache
log file there, it’s just random right? This IP address requests something, and then this
one and that one, whatever–it’s all just kind of jumbled together. A very common form
of the use of the dictionary in solving your problem is that it takes incoherent data and
it makes it coherent, it organizes it. So, for example, suppose I wanted to count how
many times each IP address had been hitting my server by looking at this log file. What
I could do is I’d say, okay, I’m going to rip through the entire file–which I’ll show
you in a second–and for each IP address, I’m going to use the IP address as, let’s
say, the key in the dictionary. And as the value, I’m just going to count how many times
I’ve seen that key. So, the first time it shows up, I’m going to put a one in there.
Maybe I could use in to kind of check if it’s there or not, to kind of boot strap this like,
the first time I put it in. And then the next time I see that IP address, I could go to
the dictionary, use square bracket, I’d say, “Oh, is this in there?” If it is, I’ll do,
you know, plus equals one or something to kind of like pump the value up, and so by
the end, I’ve gone through this unordered data and I’ve used the dictionary to kind
of associate by IP address. So, anything where you’ve got this random piece of data in one
place and you want to associate it with other occurrences of that random piece of data,
the dictionary is like, hands down the good way to do that. And it relies on this fact
that it’s very fast at this one operation, which is, given any random key, it can look
up that value very, very quickly. Now, stepping even farther outside of myself, Google really
runs as a big hash table and that’s basically what it is, right? It’s a big hash table by
word, right? And each word, kind of, points to a list of URLs or scores, or something.
So as a user, when you type in a word–you know, whatever that, you know, Britney Spears,
that’s two words, I guess. You know, really it’s going to this gigantic hash table that
is Google, it’s looking up Britney and like there’s this big list of URLs. And it’s looking
up Spears, and it does officially and then, you know, you just kind of intersect those
lists. I mean, that’s Google in that show (ph). To show that’s very clarifying, all
right.>>Where is Yahoo now?
>>PARLANTE: Yeah, no, Yahoo it’s a linear–anyway, yes. I’m–they all have–they also have hash
table technology so that’s not, that’s not the problem. All right. So, predictably the
big exercise for today which I’ll demo in a second. Yes, I mean, why don’t you use the
dictionary that’s totally appropriate thing. And in fact, dictionaries are–I mean, you
can sort of see–the subtext I was saying you–telling you is, dictionaries are an extremely
useful, and powerful construct. And so, I’m going to want you push to use them like it’s
a good thing to get practiced with. All right. So let me show you the last thing which is
files. And I think–I’m going to go back to editing for this. I’m going to show
you some files stuff here. All right, so here’s, hello, all right, so there’s just, you know–I’m
going to–there’s–In UNIX, there’s this utility “cat” and what it does is it–just, you know,
prints out the concepts of a file. So, I’m just going to go ahead and kind of recreate
cat and Python just to kind of show you how to how to open files. So, let’s say this thing
takes a filename–I’m going to write a function called “cat” and it takes a filename argument
and what I want it to do is just print the content to that file. So, the way to do this
is there’s a built-in called “open,” and it’s first argument is filename and the second
argument to this is kind of resembles other languages. I can specify an “r” here to mean,
I want to open this for reading or I could specify “w” to mean, I want to open it for
writing, whatever. This case will just–we’ll open this for reading. And there’s actually
a variant, if you put a “ru” there, it opens it in a way where it’s going to–it’ll ignore
DOS line endings versus UNIX line endings or whatever. I will kind of fix that under
the hood, so that’s nice. So, probably the simplest way to deal with–let’s say there’s
a text file–to deal with online and the files, you can actually write a for-loop over a file;
sort of like it was a list. So I can say “for line in f.” So, I loop over “f” and why is
it great, what it does is it actually reads the file in line by line and just processes
one line at a time. So, if I were to say “print line”–I mean this is why–I want to just
echo the file. So, I’ll just print each line, and then, here I’ll just–I’ll fix-up my “main”
to call this thing. So, “main” just protects whatever command line argument I have here
and it’s just going to call “cat” and just say, you print this out. So, I’ll–I’m here,
right? Okay, so let’s see. In day one–so, I’ve got this file, a small.txt, I’m going
to take that up here. Okay, so if we look at what’s in small.txt, this is a beautiful
poem I wrote for the class. So now if I’d say, “”” of small.txt–well, it’s
to me it said, so, I open that file, it’s reading it, and it’s printing it but I’m getting
this kind of line doubling; I’m not improving my poem. So, the problem is this line string,
it includes the new line at the end and then, when I print it, I’m kind of putting another
new line there. So to fix this–Python obscures some text. If you put–if there’s a trailing
comma at the end that inhibits that last new line. So, I’ll save that. I’ll just run it
again. Ah, excellent. Okay. All right, so that is one way to read a file. You open it
into this thing “f” which is kind of a file handle kind of thing, and then you just loop
over it. This technique, where you loop over line by line, it has this one virtue–sort
of going back to my apache. I could have an apache log that’s like 47 gigabytes of just
texts, and this loop hole has run through it but it will not require 47 gigabytes of
RAM. This uses a tiny bit of RAM because it deals with each line independently, that’s
an efficient case. So, if you can go line by line, this is an efficient way to do it.
Also, just for completeness, at the end there’s a dot close–I should not, you know, close
the file, you know–just to be plain (ph). If you omit it, it closes it on when the process
exits but, you know, probably more correct it and close it. All right, so that’s one
way of doing it. I’m going to make aside here, just a stylistic aside that you’re going to
need badly in about 20 minutes which is–if we were in Java or C++, we would know what
variables are strings and what variables are lists because there’s all these declarative
syntax telling you; what’s a string, what’s a list, or whatever. I want to put out–in
Python there’d be all these cues. Sort of, when you look at your own code there’d be
all these cues about what’s going on. In Python, there are no cues. You just have to keep in
your head, what’s a filename, what’s a file, what’s a string, what’s a list? Now, there’s
something you can do about this. The one thing you can do, the one thing you get in Python
is your variable names. And you knew, you were taught or whatever, well, you knew, oh,
yeah, having variable names is kind of a good idea. But in Python, it’s 10 times more important.
So, I want to point out in my little garbagey (ph) example here. And now, what I’m typing
the stuff in the interpreter. A lot of times I use one variable names but I’m a little
more disappointed here in the editor. This thing I spelled out–yes, that’s a filename
not a file, not a list string, it’s a filename. It’s very useful in Python that you name the
variables to kind of keep track of what is that. And very often when I’m walking around
standing behind people, many of the bugs I see is where you kinds off by one. You sort
of lost the scent. You’re like, “Oh, this–you know that’s the filename.” “Oh, no, it turns
out that’s a line from the file or it’s list of all the file in there.” You kind of get
this off by one. Of like, “Wait what does that variable contain?” because you’ve got
this natural progression of filename, to file, to line of text, to word, or whatever. It’s
very easy to get off by one of where you are in that progression. And Python, the only
thing you have is the variable names. So, I’ve worked with a lot people, you know, debugging,
basic Python programs and I’ll tell you, it is–it pays off very well to be conscious
of giving your variables good names of like what is that? Is that a string? Is that a
list? Is it a dictionary; whatever. And certainly in my solutions, whatever, you know, I fall
that, I mean, that’s just good style anyway, but in Python it happens to pay off especially
well because you’ve got so what else is going on. All right, so on our bigger exercise today
this will, this will certainly come up. The other way that this comes up is whenever I
have a list of things. I’ll try and give it a variable name ending in s words, or lines,
or something like that to sort of like cue me like, “All right, that’s the lists of things.”
Okay, end of editorial; it’s actually good advice. So, my second favorite Python file
primitive is there’s this function I think–the capitalization I remember, I think it’s “readLines”
like that. I guess we just try it. And what that does, is it reads the entire file into
memory as a Python list of lines where each element of the list is one line from the file.
So, then here–so for cat, I could just say “print lines” I guess and it just be done.
All right, I’ll try this to just check if I have the name right there. Has no attribute
“readLines” okay, apparently not. Maybe, it’s lowercase L, it must be. Oh, excellent. All
right, so now you can see just–so now it’s a Python list. So, now you could loop over
that list, do something or whatever. So, if you had a file with like, you know, 10,000
or something rather is that you want you process as a list, you know, this is a–one easy way,
you just pull it and ran in one step. Notice, if the thing is 28 gigs of data, now this
does at least 28 gigs of RAM to store like I really am just drawing the whole thing around.
But, you know, I get, I get very–you know give you an access to it. My absolute favorite–I
know you’ve been very curious. What is my favorite Python file primitive? Oops, and
it’s just–there’s this one just called “read” and what is does, is it reads the entire file
into one string. And I know that’s it, but for some problems that is just so convenient.
There’s no notion of like looping this line versus that line I just, like suppose you
wanted to do big, some big suture place operation on a file or say some regular expression processing.
Yeah, just having the entire thing is like one big string is phenomenally convenient.
So, that is, I think that’ll just work. Yes, check it out. So, we’ll build on that one
a little bit more later on. I think for today just the very–the first one I showed you.
Just for line in “f.” Now, that’s probably the most common one. Also going back to my
ranting editorial. By variable, noticed? When I–yes, read into variable called text like
I’m trying to remind myself like, oh, right, you know, that’s the whole text, whatever.
All right. So we’ve got dictionaries. We’ve got files; these are the last two elements
that you needed to know right–there’s kind of an inflection point, where like with all
the stuff I’ve showed you now, you can write just like real Python programs. And so that,
that’s why I like, last exercise is going to look at–look like. I already gave you
the advice about variable names. One other piece of advice I should give you. I’m about
to demo some larger programs for you that I want you to implement and it is the–sometimes–or
at Stanford, right? If I’m talking some 17 year old–what they will do is they’ll type
in the entire program, like, well, here’s my vision of how the entire program is going
to work, and then once they type in the entire thing in, then they try running it. And then
they like, you know, of course, it crashes on my client too early. That is not the way
to do it, especially not in Python. Python is so good and you make a little change and
then you can run, and you can see immediately kind of what’s going on. So you want to sort
to keep that focus right at the kind of growing edge of your code. And there’s two things
that are going to help you out here; let’s say–so for your next problem, you’re gonna
do these things that involve like reading a file, then processing lines and for each
line you’re going to want to kind of do something. What you should do is to move very incrementally,
like re-read in the lines and well the first thing I just want to print each line. So you
just print each line and then after you print it and, you know, when you’re done, you could
call like sys.exit or something, just like, okay we’ll just bail out. And just get that
working through like, no now, it’s pretty [INDISTINCT]. So it’s okay, well, what’s my
next goal? My next goal is, you know, I want to find all the words, so I’ll just print
each word or whatever. And so just have the program print what your kind of next goal
is and keep iterating until it’s printing the right thing. And Python–because Python
is very easy to edit and it’s built-in printing facility is actually quiet good, right? You
can print a dictionary, you can print a list, all that stuff; there’s no code in your carbon
card. It just prints, it just–it’ll adopt something kind of reasonable to the console.
And so you can use that to kind of iterate very tightly and certainly as I walk around,
ask and answer questions, the same thing I’ll do. So, that’s why–have a goal, print what
you have, [INDISTINCT], some of it–it’s kind of nice if you print what your data structure
has kind of a step in of solving this thing, seeing the pixels of like, “Oh, I have a list
of strings or whatever,” can help your imagination think of like, “Okay, well, what’s my next
step? Oh, now I need to make a list of, you know, a dictionary or something.” So it’s
so nice to be all just to see your data structure right there. And I guess more broadly, what—you
know, why is it that Python program was given this zone of like, “Wow, they’re very productive,
they can just get stuff quickly.” It’s partially because not just that they know the Python
language but that their program in a style that fits the things Python is good at, so
this is the right stuff for today. Okay, enough kind of heavy device, let’s talk about actual
work. Okay, so I’m going back down to the day 1 directory, and there are—I’m gonna
show you two programs, all right? As before, this program–so the first one I will show
you is a word count. It’s the first exercise for today, this is what I want you to do today,
and I’m going to demonstrate very quickly a second exercise which you could do if you
just don’t like, you wanted more practice or whatever. But word count’s the one I wanted
to work on. So I’m going down to my solution directory, so I can actually demo working.
So what word count does, is if you–oops, ignore that hey there thing, that’s left over
for something else–so what it does is you’re given a file and what I want you to–I’ll
just run it here, and I’ll run it on that small file–oops, I’m sorry–it takes a command
line argument, in this case a dash, dash count, and what this does is I want you to go through
the file, I want you to find all the words, and I want you to just count and I want you
to convert them with all to lower case, so we won’t count upper case, smaller case different.
I want you to just count how many times each one appears. Now to find the words, there’s
this Python built-in–which I showed you before, I’ll show you again–so I have like aaa bbb
ccc, there’s dot split and I’ll show you this dot split before I would like a corn or something.
It turns out if you call dot split with no arguments then it splits on white space, and
that’s going to turn out to be a pretty reasonable behavior for this program. So for word count,
I’m just looking for split with no arguments so you just get the word and it’s just automatic–it
knows what it’s have is, what a new line is, it’ll do something kind of original. Tomorrow
with regular expressions, we’ll do a better job but for today this is [INDISTINCT]. All
right, so what I want you to do is process the whole file and like a fair with the words
are, and then you can debug on small.text, and that’s sort of more fun. Then we also
just have the entire text of “Alice in Wonderland” and so you could just process that as well.
Something a little dopey is happening here well, like the word while appears 20 times,
but the word while followed by a comma appears four times. This is just because of the split
strategies just on white space and it’s not smart enough to trim off anything else. Okay,
I apologize this just, this just to get us through today. Tomorrow, I will show you how
to deal with the punctuation as well, but for today, I think just deal–we’ve got enough
problems just with the dictionary. Well, I want you to learn the dictionary in the file.
So one thing’s that’s need to out this is, Python is not known for being especially fast,
it’s known for being quick with your time as a programmer, it’s you know, it’s a great
instrument and you can get stuff done very quickly. But you know memory in anywhere else
is not that quick. That’s just you know, you should know, that’s one of the things you
know the truth. And yet, I just process the entire “Alice in Wonderland” and like, whatever,
if your time that says like it’s about 28th of a second and this code is just written
in the most obvious convenient way–the laziest way I can think of, which is of course the
way [INDISTINCT]. So on the one hand, you know, Python is not the quickest language;
on the other hand, most things are just kind of I/O bound like probably saving that last
inter second CPU time, maybe not the best usage of your time or you just want stuff
to work so that will sort of show up here. All, right, so that is part A, counting the
words. Then—and I should mention the parsing of the command line arguments and the other
kind of boilerplate, I provide for you. So when you look in that word count file, you’ll
see there’s a boilerplate that’s done for you and then you’d figure out what just the
part of you need to add. So then I want to have top count–oops, what’s two top count
on “Alice in Wonderland?” Do you guys have a 28th of a second to spare? Sure, all right.
All right, so what does that do? Yes, it’s sort of–it’s by the frequency. Yes, so–what
appear most often. Now, just in terms of writing code, well, this both use a dictionary which
has the word as the key and the count as the value. I don’t want to have one copy of the
code that builds that dictionary for dash, dash count and another copy of the code that
builds it for dash, dash top count. Really, you should have one copy of the code that
builds the dictionary, either by putting into a separate function or, you know, or you could
[INDISTINCT] but I want one copy of that code that builds the dictionary and then we have
these two uses of the dictionary, either you could loop to the dictionary and you just
print all the words in alphabetical order or you could go to the dictionary and so the
trick here is, it’s like, “Oh, I don’t want all the words, I want to pick out the words
that have the big counts and I want to print those and in sort of order by count.” So for
that problem, you kind of want to use the dot items on the dictionary, where you can
pull out all those two poles and then made this some custom sorting, right where you
want to sort the two poles now at the big second number, anyway, that’s part B. So the
first problem is part A. All right, I have one more thing to show you, this is whole
other program, the mimic program. And I’ll just run this on “Alice in Wonderland.” Let’s
see what does this say? “Alice’s shoulder, and birds with some minutes, the only grinned
a stop to death quote. You might do something splashing about at the Caterpillar.” What
is this? Yes, you could–well, so actually you can run this–so, all right. So I’ll tell
you what this program does. It’s a fun program, it uses actually in terms of coding technique,
it’s very similar to word count. Same level of obstruction, it just does something different.
What this program does and also it shows how Python is actually quite fast sometimes. It
looks at every word that appears on the text and for every word it just create keeps a
Python list of all the words that ever appear after it in the entire text. You can sort
of imagine building a Python dictionary that’s just sort of attracts this. So for the word
sister, I have a list of all seven words that ever appeared after the word sister in the
text. So that once you have that data structure you could just pick a random words, so I’m
just going to start with Alice’s, and I look at the list of the words that ever appeared
after that and I just pick one at random. So apparently in this case I got shoulder
comma and then for shoulder comma, I look at the words that ever appeared after that
and I just–it’s just totally random. And yet, you can–it’s sort of weird, you can
I mean it’s not completely believable but it’s sort of weird for one unbelievably primitive
strategy this is, I mean, you can end up mimicking some text. So you can have fun if you run
it on Google design docs. The other thing that you can do of this–only a computer sciences
can prove it is you can write it on Python text, and it sort of like it’s some random
sense like my variables and comments and stuff. I mean the line breaks are completely messed
up. So, that is–so if you have time or extra energy to kill, you could take a look at the
mimic program but really what I want you to work on is the word count program. And that
is the lesson for today. So, please go ahead. Get start on that, I mean, if you want to
keep working on the list once earlier or once–I’m happy to answer questions about that. But
this is a nice kind of a threshold like, oh now, this is really all the pieces of a real
Python program you put together, so it’s a nice exercise to work on.

100 thoughts on “Google Python Class Day 1 Part 3

  1. @1000blabbities yes, it wont let me post the link, but just google "google-python-class exercises" then DL the file

  2. i really like this fast-talk instructor. the lessons just flow. all the things become clear and easy all of a sudden.

  3. i guess some people just start worshiping whatever is "hot" in the world. They need be reminded that smart people existed even before google and they don't have to be with google.

  4. lol , I liked that he used his function Cat to print "Roses are red, Violets are blue, all of my base are belong to you!".

    (Poem is a reference to the character Cats in the game Zero Wing who termed the phase "All your base are belong to us!".)

  5. I like the captions for being deaf…but what about the last half of the Chapter and especially at the very endmost of the video!?!? I don't recall being walked through on those parts !!!!!!!!

  6. please tell me how to run the program while in pyshell…
    the way you run it is different than what I do..

    for me to write the program, I've got to open up a new window and do my codings there then save then CTR+F5, run module…

    but what you do is different, those $python thing, doesn't work on my py2.7
    I tried as best as I can but I can't mimic the way you code and the way you actually run it in pyshell.

  7. you might be in the wrong directory in your command line. you need to use the cd command (for "change directory") to get into wherever your python script is on your computer, then you'll be able to run it with the "$python" syntax.

    there's a great tutorial on working with the command line that helped me a bunch. the guy's website is Learn Code the Hard Way (dot com). Look around for the CLI or command line crash course. his python tutorials are pretty solid as well.

    good luck!

  8. readline() != readLine()… that's why an IDE with text completion is the way to go. Why waste those brain cells memorizing the exact syntax? Especially when you are going to learn 5-6 languages each with a unique syntax over your career?

  9. how the hell do you do the exercises , I got the python cmd thing going, and I downloaded the exercises from the website now what do I do ? please help!

  10. Open the exercise in IDLE. you'll probably have to find his print lines and put parens around the contents.
    IE) print 'donuts' –> print('donuts')

  11. I'm sitting on & looking for the Alice in Wonderland Text file you ran the dictionary functions on but I'm unable to find a link. I'd like to take a look at

  12. Its crazy how good this teacher is!!! I love this, it literally saves my life. Thanks a lot.
    What does google have to do with these classes anyways?

  13. Google's technologies use Python a fair bit, if you take a look at a Google job listing for a Software Engineer Python will be mentioned somewhere

  14. actually retrieval from a dictionary-hashmap is not done in constant time but in O(logn) time, where n is the size of the dictionary

  15. also n^3 and 2^n are constants for a given n, so what's the point of complexity theory if you always end up with "it's constant" ?

  16. 1) for hashmap if the data is uniformly distributed over the hashcode, then the time complexity is still O(1), if no so, worst case O(n). This somehow depends on a good choice of hash function.

    2) Keys in Hashmap is not sorted but they are sorted in treemap.
    if your task is just search ONE element, hashmap is better than treemap. However, if you are doing a range search. "find age between 26 and 30". Treemap will be a better choice. That's why B+tree is used by many databases.

  17. let T(n) be the time complexity as a function of data size n.
    the point of complexity theory is not to measure T(n) at a particular value n but rather to calibrate the growth rate of T(n) as n grows.

    n=3 n^3 = 27 2^n=8
    n=10 n^3 = 1000 2^n=1024
    n=1000 n^3 = 10^9 2^n ~= 10^100

    so polynomial solutions are much better than exponential ones.

  18. 13:05 to 13:10
    anyone know how to do that in powershell?
    (when he says open of small.txt)
    I've searched and searched but I guess my terms aren't optimal.

  19. i see some people are having trouble running this in the terminal. first you must enter the correct directory where the file is located, easiest way to do this is:

    1. Open terminal
    2. type 'cd '
    3. Open finder and find the "basic" folder, it's inside of the "google-python-exercises" folder
    4. Drag the "basic" folder into the terminal. This will paste the file path. 
    5. Press enter

    Now you're in the correct directory. Next, once your code is ready to be tested:

    1. type './ –count small.txt' into terminal, this will test the "print_words" function on the "small.txt" file in that directory.

    2. type './ –topcount small.txt' into terminal, this will test the "print_top" function on the "small.txt" file in that directory

    If you want to test your code on the "alice.txt" file, just change "small.txt" to "alice.txt" 

  20. I have very nonsence question. Why the code is commented with '##' in all of this tutorials ? According to Python documentation '#' is enough to comment a single line.

  21. is not correct. You find all the stuff here:

  22. in the video it is said that by using we can read the file as one big string but a string terminates when it encounters a n then how does it read the entire thing…..plzz reply

  23. I tried to do the word count, but I have a problem with non alfanumeric characters, I tried this function found online
    wordsList=[''.join(c for c in fileText if c.isalnum() or c.isspace()).split()]
    where fileText is the string read from the file, I tried the same line in shell and it does return the string split and without special characters, but when I try this line in code:
    for elem in wordsList:
        if elem in dictionary:
    it says that 'list object has no atribute split'
    can you help me?

  24. Is there a way to create dicts of dicts in python similar to creating a map of a map in python? wherein the value would act as dict itself for another dict.

  25. Hi,
    Can someone tell me what the following command does?
    if not word in word_count:
    word_count[word] = 1

  26. I am having issues with sys.argv[1] ,even in the first video as well it dint always pops up the error and here as well it does not open up the file.Can anyone help?

  27. I understand most of what you did. my problem is what can I actually do with Phyton how do I use it to create things etc I'm learning this in advance as I'm soon going to college to study it more but I'd like to see what it does or how I can use it to build apps etc

  28. This comment is for linear merge question in

    # E. Given two lists sorted in increasing order, create and return a merged
    # list of all the elements in sorted order. You may modify the passed in lists.
    # Ideally, the solution should work in "linear" time, making a single
    # pass of both lists.
    def linear_merge(list1, list2):
    # +++your code here+++

    My suggestion would be to use following answer:

    def linear_merge(list1, list2):
    # +++your code here+++
    list = list1 + list2 # Add multiple lists into new list
    return sorted(list) # Sort the new list

  29. can you please explain what is this if condition doing

    if not word in word_count:
    word_count[word] = 1
    word_count[word] = word_count[word] + 1

    this is from

  30. i have just started with Python and these are my first videos, and i am enjoying it. thanks for making it public.

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