RandomPythonTricks.md

I found a notepad where I had collected what appeared to be a random assorted of Python "tricks". I didn't have a source documented, but I'm sure these things are floating around the internet. If I encountered your trick by browsing your blog post or Stack Overflow answer, thanks!

Debugging

import pdb; pdb.set_trace()
python -i foo.py; import pdb; pdb.pm()

Profiling

python -m cProfile my_script.py

Safer Evals

expr = '[1, 2, 3]'

# Don't do
my_list = eval(expr)

# Rather do
import ast
my_list = ast.literal_eval(expr)

Sorting custom objects

users.sort(attrgetter("username"))

Boolean Values as dict Keys

a = {True: 0, False: 1}

List Tricks

# Reversing a list
mylist[::-1]

# The built-in reversed is faster and returns an iterator
# because the above is a shallow copy of mylist

# Resetting a list
l[:] = [1, 2, 3]

# Copying a list
y = x[:]

Pro-tip: the built-in enumerate takes a starting index parameter!

Cute Fizz Buzz

['Fizz'*(not i%3) + 'Buzz'*(not i%5) or i for i in range(1, 100)]

Cute Factorial

from operator import mul

factorial = lambda x: reduce(mul, xrange(2, x+1), 1)

Pro-tip: verbose regex can be broken over multiple lines or use string concatentation.

Other useful things

• Descriptors
• Metaclasses
• namedtuples