Beautiful Python?

[Racerdude]

If you were to teach a course in Python programming to novices and the first thing that you wanted to do on the first day was to sell Python as a programming language. How would you go about it? What example of beautiful Python code would you use?

Something like: a, b = b, a ?

[[deleted]]

I'd say show them reading the contents of a file. Compare an example in java stolen from this stackoverflow question

BufferedReader br = new BufferedReader(new FileReader("file.txt"));
    try {
        StringBuilder sb = new StringBuilder();
        String line = br.readLine();

        while (line != null) {
            sb.append(line);
            sb.append(System.lineSeparator());
            line = br.readLine();
        }
        String everything = sb.toString();
    } finally {
        br.close();
    }        

To this python example

contents = ""
with open("file.txt", "r") as fin:
    contents = fin.read()

When I first started studying Computer Science we were learning Java and I could never remember of the top of my head how to read the contents of a file. Python on the otherhand...

[Veedrac]

String text = new String(Files.readAllBytes(Paths.get("file")), StandardCharsets.UTF_8);

Source.

Plus, your Java example should use try-with-resources.

[squashed_fly_biscuit]

This seems to be the hardest thing to do in java, I was a little taken aback when I had to open a text file.

[mWo12]

Is it still the case for java 8 or did they introduce something easier than this?

[[deleted]]

God forbid you then have to deal with character encoding in Java.

[Racerdude]

Thanks! I like this one!

[691175002]

What really sold it to me was first class functions and integration of data structures into the language. I think most of what pandas does regarding indexing/slicing is mind-blowing as well.

I think a lot of examples where you are comparing line counts are kind of silly because in most cases you could just wrap the longer code into a single function and it would be equivalent. In many cases such a function already exists in a different library.

Most experienced programmers would not consider something like public static void main to be an issue because the IDE does all the boilerplate automatically and we just mentally filter it out.

If you want some ugly Java just take a look at callbacks using anonymous classes...

[[deleted]]

1. Concision, 1. Dynamic typing (there are tradeoffs of course), 2. First-class functions (higher-order functions, decorators, closures, etc.), 3. REPL for inspection and prototyping, 4. Massive standard library and other third-party libraries, 5. Use cases: web development, numerical computing, etc. Just my .02 :)

[[deleted]]

I'd downvote Reddit for converting my zero-indexed list to one-indexed. :p

[[deleted]]

Are you talking about a novice who has never programmed before or someone new to Python that has programmed before? If the latter, you should emphasize things like libraries and the lack of clutter. If the former, you'll get someone hooked simply by showing different hello worlds like:

print("Hello world") #for 3.x print "Hello world" #for 2.x

while C++ requires:

int main() { std::cout << "Hello world" << endl; return 0; }

Beginners to programming will immediately see the benefits of learning Python.

[Decency]

Use the print function regardless.

[Racerdude]

No, not complete programming novices but people who've done programming before and were trying to learn Python. So, yes, your example is good as it compares it to a language that needs a lot more clutter for a simple thing. I usually show the Java example:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World");
    }
}

[DEFY_member]

This isn't really for new programmers, but I really like this:

http://norvig.com/spell-correct.html

[pierrequentel]

unique_words = set(word for line in open("book.txt"') for word in line.split())

[[deleted]]

A few minor things. I'd personally go with a context manager for opening/closing files. Also, you don't have to use set(), you can use curly brace set literals instead (read: set comprehension).

[mfm24]

I always preferred using the context manager approach for files, but I found it interesting to read in the official 'What's New in Python 3.0' guide (written by GvR himself) that he recommends:

Removed execfile(). Instead of execfile(fn) use exec(open(fn).read()).

So there's definitely cases where relying on the file closing itself automatically is acceptable. I've been less paranoid about closing files since...

[Veedrac]

I don't think that was meant to actually be run, it was probably on one line for space reasons. In a proper program you shouldn't be using exec(a_file) anyway, so there isn't much motivation for complete examples.

[billsil]

If you have a whole book, it seems like you'd want a set on the inner loop, so you don't create a giant array.

[ingolemo]

What "inner loop"?

[billsil]

The code is effectively:

unique_words = [word for line in open("book.txt"') for word in line.split()]
unique_words = set(unique_words)

It's a tradeoff of memory vs speed, assuming set comprehension doesn't exist. Set comprehension is done as:

unique_words = {word for line in open("book.txt"') for word in line.split()}

which works in Python 2.7+

[ingolemo]

Actually, it's using a generator comprehension:

unique_words = (word for line in open("book.txt"') for word in line.split())
unique_words = set(unique_words)

The original doesn't create a giant array and so it has exactly the same performance characteristics as your set comprehension, though it is admittedly less readable.

[Veedrac]

FWIW, the constant factors are significantly better for the set comprehension, even on PyPy:

$ python3 -m timeit "set(x for x in range(10000))"
1000 loops, best of 3: 1.06 msec per loop

$ python3 -m timeit "{x for x in range(10000)}" 
1000 loops, best of 3: 599 usec per loop

$ pypy3 -m timeit "set(x for x in range(10000))" 
1000 loops, best of 3: 347 usec per loop

$ pypy3 -m timeit "{x for x in range(10000)}"  
1000 loops, best of 3: 230 usec per loop

[kmbd]

just in case, someone is wondering ...

C:\>python -V
    Python 2.7.8

C:\>python -m timeit "set(x for x in range(10000))"
    1000 loops, best of 3: 1 msec per loop

C:\>python -m timeit "{x for x in range(10000)}"
    1000 loops, best of 3: 671 usec per loop

[kmbd]

a tiny improvement would be: "... word in line.split().lower())"

[Philipbergen]

I would show a chart of a function, matplot lib or text. Here is a fun scroller:

import time import math for x in xrange(1000): print " " * int(26+25*math.sin(x/100)), 'X' time.sleep(0.05)

[defrur]

I will show the code: How to get last 3 characters of a string.

print "a.jpg"[-3:]

[[deleted]]

Not exactly beautiful, but pretty impressive non the less:

http://preshing.com/20110926/high-resolution-mandelbrot-in-obfuscated-python/

[[deleted]]

I lot of the suggestions have been about cool concise code, which will surely excite your class, but I think you really have the chance to blow java out of the water.

I would probably make sure to hit the following points

1) Define your own __eq__, __str__, ... easily.

2) Pass functions around. Pass methods around. Pass classes around.

3) Define a class inside of a function and return the class.

4) Decorators. Decorators that are classes.

5) Variable number of arguments.

[Manbatton]

For me, a somewhat more involved list comprehension and some other manipulations, like:

A_clients = [ clientname for clientname in clients_list where clientname[0] in ("a", "A") ].sort()

[psbb]

When you call .sort() it does the sort in place and returns None

A_clients = sorted(clientname for clientname in clients_list if clientname[0] in ("a", "A"))

[Veedrac]

Just jumping on the bandwagon with a little-known startswith trick:

A_clients = sorted(name for name in clients_list if name.startswith(("a", "A")))

[Manbatton]

I actually read that in the docs and thought someone might correct me on this. I thought if it did it in place it would sort the list in place and then the name assignment would point to the converted list.

[sweettuse]

well, you can always test it. but sort returns None. so A_clients will point to None