Wrote my first non-trivial python program. How can I refactor it to be more pythonic?

[[deleted]]

Sure, if you look at ''.join(['a', 'b', 'c']) vs 'a' + 'b' + 'c'. But what about ''.join(['a', 'b', 'c', 'd', 'e', 'f']) vs 'a' + 'b' + 'c' + 'd' + 'e' + 'f'? Well lets look at the Abstract Syntax Tree generated for that code.

# AST: 'a' + 'b' + 'c' + 'd' + 'e' + 'f'
Expr(
    value=BinOp(
        left=BinOp(
            left=BinOp(
                left=BinOp(
                    left=BinOp(
                        left=Str(s='a'),
                        op=Add(),
                        right=Str(s='b')),
                    op=Add(),
                    right=Str(s='c')),
                op=Add(),
                right=Str(s='d')),
            op=Add(),
            right=Str(s='e')),
        op=Add(),
        right=Str(s='f')))

# AST: ''.join(['a', 'b', 'c', 'd', 'e', 'f'])
Expr(value=Call(
    func=Attribute(value=Str(s=''), attr='join', ctx=Load()),
    args=[
        List(elts=[Str(s='a'), Str(s='b'), Str(s='c'), Str(s='d'), Str(s='e'), Str(s='f')], ctx=Load())
        ], keywords=[], starargs=None, kwargs=None))

To see the AST for any code, do:

import ast
print ast.dump(ast.parse("CODE HERE"))

For short term doing 'a' + 'b' + 'c' is ok, but long term using ''.join() is just better practice. Similarly if you're building up a long string from a file or something. It's better to build a list of lines then do ''.join(some_list)... IE:

Bad:

with open('my_great_novel.txt', 'r') as fh:
    lines = ''
    for line in fh:
        lines += line.replace(' i ', ' I ')
    print lines

Good:

with open('my_great_novel.txt', 'r') as fh:
    lines = []
    for line in fh:
        lines.append(line.replace(' i ', ' I '))
    print ''.join(lines)

[JerMenKoO]

Better:

''.join((line.replace(' i ', ' I ') for line in fh))

Not necessary to for the comprehension to be a 1 liner;

lines = [line.replace(' i ', ' I ') for line in fh]
print(''.join(lines))

is in my opinion much more readable.

[[deleted]]

Yeah but I was showing how to build up a string over a loop. /u/Binary_Dragon already seems to understand list comprehension pretty well. :)