Idiom #1¶

Use tuples to swap values! In python, you do not need to create temp value when swapping variable values. They can be done in one line by using tuples.

# bad
temp = old
old = new
new = temp

# good
old, new = new, old

Idiom #2¶

Don't use indices when looping. In python, you do not need to keep track of indices when looping.

states = ["texas", "california", "ohio", "florida"]

"""
# bad
i = 0
while i < len(states):
    print(states[i])
    i += 1
"""

# good
for state in states:
    print(state)

texas
california
ohio
florida

Idiom #3¶

Use 'enumerate' when you need to use the index.

# For the same example as above, what if you REALLY need to use the index? Here is how to do that:

states = ["texas", "california", "ohio", "florida"]
for index, state in enumerate(states):
    print(index)
    print(state)

0
texas
1
california
2
ohio
3
florida

Idiom #4¶

Use 'zip' to loop over two lists.

# What if you wanted to loop over two lists at once? Zip is the function to do just that.
states = ["texas", "california", "ohio", "florida"]
weather = ["hot", "medium", "no_idea", "hot"]
for weather, state in zip(weather, states):
    print(weather + ' in ' + state)

hot in texas
medium in california
no_idea in ohio
hot in florida

Idiom #5¶

Use 'izip' for long lists. 'zip' constructs the new combined list before entering the loop. For long lists, this new list can consume a lot of memory. Instead, use 'izip' which constructs the new list on-the-go.

Note: In python 3, zip returns an iterator. iZip does not exist in python 3.¶

states = ["texas", "california", "ohio", "florida"]
weather = ["hot", "medium", "no_idea", "hot"]
for weather, state in izip(weather, states):
    print(weather + ' in ' + state)

Idiom #6¶

Use 'join' to join strings together. Strings have a built-in function called 'join' that can be used to concatenate them.

sample = ['my', 'name', 'is']

"""
#bad
sample[0] + ' ' + sample[1] + ' ' + sample[2]
"""

# good
' '.join(sample)

'my name is'

Idiom #7¶

0 is False and everything else is True. Any string, list, array or dict with length > 0 is True. This applies to many other languages as well.

sample = ['mom', 'dad']
stri = "hi"
count = 0

"""
# Bad

if len(sample)>0:
    print('hi')

if len(stri)>0:
    print('hello')
    
if count == 0:
    print('nothing')

"""

# good

if sample:
    print('hi')

if stri:
    print('hi')

if not count:
    print('nothing')

hi
hi
nothing

Idiom #8¶

Use 'format' for string formatting. It's easier to read and less prone to error.

character = 'Neo'
movie = 'Matrix'
actor = 'Keanu'

"""
#bad

print('%s played %s in %s.' % (actor, character, movie))

"""

# good

print('{actor} played {character} in {movie}'.format(actor=actor,
                                                    character=character,
                                                    movie=movie))

Keanu played Neo in Matrix

Idiom #9¶

Use list comprehensions to generate a list. Most of the times, they are easier to read and require fewer words.

states = ["texas", "california", "ohio", "florida"]

"""
# bad

new = []
for state in states:
    if 'a' in state:
        new.append(state)

"""

# good

new = [state for state in states if 'a' in state]

print new

['texas', 'california', 'florida']

Idiom #10¶

Generators are a powerful concept in python. Instead of having a function which returns a huge list at once, use generators to return one value at a time as it's called. Creating a generator is easy, just use 'yield' instead of 'return'. A key thing to remember is that a generator returns a generator object which is an iterrator.

Note: In python 3, range returns an iterator.¶

# Function for getting a list of numbers
# This function will return a generator
import datetime as dt
def get_range(num):
    for n in range(0,num):
        yield n

print get_range(5)

<generator object get_range at 0x10410df50>

# call the generator object so we can iterate over it
for num in get_range(5):
    print(num)

10 python idioms to help you improve your code