What do you wish you'd known about when you started learning Python? [closed]

Answer 1

Two brain-cramping things. One of which doesn't apply to Python 3.

a = 095

Doesn't work. Why? The leading zero is an octal literal. The 9 is not valid in an octal literal.

def foo( bar=[] ):
    bar.append( 1 )
    return bar

Doesn't work. Why? The mutable default object gets reused.

Answer 2

• What enumerate is for.
• That seq = seq.append(item) and seq = seq.sort() both set seq to None.
• Using set to remove duplicates.
• Pretty much everything in the itertools and collections modules.
• How the * and ** prefixes for function arguments work.
• How default arguments to functions work internally (i.e. what f.func_defaults is).
• How (why, really) to design functions so that they are useful in conjunction with map and zip.
• The role of __dict__ in classes.
• What import actually does.

Answer 3

I wish I knew well a functional language. After playing a bit with Clojure, I realized that lots of Python's functional ideas are borrowed from Lisp or other functional langs

Answer 4

One of the coolest things I learned about recently was the commands module:

>>> import commands
>>> commands.getoutput('uptime')
'18:24  up 10:22, 7 users, load averages: 0.37 0.45 0.41'

It's like os.popen or os.system but without all of the DeprecationWarnings.

And let's not forget PDB (Python Debugger):

% python -m pdb poop.py

Answer 5

Sequential imports overwrite:

If you import two files like this:

from foo import *
from bar import *

If both foo.py and bar.py have a function named fubar(), having imported the files this way, when you call fubar, fubar as defined in bar.py will be executed. The best way to avoid this is to do this:

import foo
import bar

and then call foo.fubar or bar.fubar. This way, you ALWAYS know which file's definition of fubar will be executed.