ruk·si

🐍 Python
Control Structures

Updated at 2017-01-03 01:22

if-statement.

x: int = 10

if x > 0:
    print('over zero!')
elif x < 0:
    print('under zero!')
else:
    print('zero!')

if can be used as an expression.

greeting = 'Hello!' if 4 > 5 else 'Yo!'
assert greeting == 'Yo!'
assert ('yes!' if 3 > 2 else 'no!') == 'yes!'

Prefer truthy and falsy checks. In Python world, this is a common practice.

name = 'Safe'
pets = ['Dog', 'Cat', 'Hamster']
owners = {'Safe': 'Cat', 'George': 'Dog'}

# bad
if name != '' and len(pets) > 0 and owners != {}:
    print('We have pets!')

# good
if name and pets and owners:
    print('We have pets!')

Use implicit line joining of () to form multiline condition statements.

width: int = 100
height: int = 0
color: str = 'red'
emphasis: str = 'strong'

if (width and not height and
        color and emphasis == 'strong'):
    print('Nice work!')

Prefer try over if. Catching exceptions is cheap in Python and will result in more pythonic code.

from typing import Dict

# bad
d: Dict[str, str] = {'x': '5'}
if 'x' in d and isinstance(d['x'], str) and d['x'].isdigit():
    value = int(d['x'])
else:
    value = None

assert value == 5

# good
d: Dict[str, str] = {'x': '5'}
try:
    value = int(d['x'])
except (KeyError, TypeError, ValueError):
    value = None

assert value == 5

Sources