十个有好python惯用法

1. Make a script both importable and executable(使你的脚本可输入且可执行)

if __name__ == '__main__':

Example

def main():

    print('Doing stuff in module', __name__)

if __name__ == '__main__':

    print('Executed from the command line')

    main()

$ python mymodule.py

Executed from the command line

Doing stuff in module __main__

>>> import mymodule

>>> mymodule.main()

Doing stuff in module mymodule

2. Test for “truthy” and “falsy” values(测试采用真假判断)

if x:

if not x:

Example

# GOOD

name = 'Safe'

pets = ['Dog', 'Cat', 'Hamster']

owners = {'Safe': 'Cat', 'George': 'Dog'}

if name and pets and owners:

    print('We have pets!')

# NOT SO GOOD

if name != '' and len(pets) > 0 and owners != {}:

    print('We have pets!') 

3. Use in where possible(如果有可能尽可能使用in)

Contains:

if x in items:

Iteration:

for x in items:

Example (contains)

# GOOD

name = 'Safe Hammad'

if 'H' in name:

print('This name has an H in it!')

# NOT SO GOOD

name = 'Safe Hammad'

if name.find('H') != -1:

    print('This name has an H in it!')

Example (iteration)

# GOOD

pets = ['Dog', 'Cat', 'Hamster']

for pet in pets:

    print('A', pet, 'can be very cute!')

# NOT SO GOOD

pets = ['Dog', 'Cat', 'Hamster']

i = 0

while i < len(pets):

    print('A', pets[i], 'can be very cute!')

    i += 1

4. Swap values without temp variable(交换两个数不适用temp中间值)

a, b = b, a

Example

# GOOD

a, b = 5, 6

print(a, b) # 5, 6

a, b = b, a

print(a, b) # 6, 5

# NOT SO GOOD

a, b = 5, 6

print(a, b) # 5, 6

temp = a

a = b

b = temp

print(a, b) # 6, 5

5. Build strings using sequence(使用序列的方式来得到字符串)

''.join(some_strings)

Example

# GOOD

chars = ['S', 'a', 'f', 'e']

name = ''.join(chars)

print(name) # Safe

# NOT SO GOOD

chars = ['S', 'a', 'f', 'e']

name = ''

for char in chars:

    name += char

    print(name) # Safe

6. EAFP is preferable to LBYL(大概意思是说使用专业的容错机制)

“It's Easier to Ask for Forgiveness than Permission.”

“Look Before You Leap”

try: v. if ...:

except:

Example

# GOOD

d = {'x': '5'}

try:

    value = int(d['x'])

except (KeyError, TypeError, ValueError):

    value = None

# NOT SO GOOD

d = {'x': '5'}

if 'x' in d and

    isinstance(d['x'], str) and

    d['x'].isdigit():

    value = int(d['x'])

else:

    value = None

7. Enumerate(常用该函数，得到(index, value))

for i, item in enumerate(items):

Example

# GOOD

names = ['Safe', 'George', 'Mildred']

for i, name in enumerate(names):

    print(i, name) # 0 Safe, 1 George etc.

# NOT SO GOOD

names = ['Safe', 'George', 'Mildred']

count = 0

for name in names:

    print(i, name) # 0 Safe, 1 George etc.

    count += 1

8. Build lists using list comprehensions(使用列表合成新的列表)

[i * 3 for i in data if i > 10]

Example

# GOOD

data = [7, 20, 3, 15, 11]

result = [i * 3 for i in data if i > 10]

print(result) # [60, 45, 33]

# NOT SO GOOD (MOST OF THE TIME)

data = [7, 20, 3, 15, 11]

result = []

for i in data:

    if i > 10:

        result.append(i * 3)

        print(result) # [60, 45, 33]

9. Create dict from keys and values using zip(尽可能使用zip()函数创建字典)

d = dict(zip(keys, values))

Example

# GOOD

keys = ['Safe', 'Bob', 'Thomas']

values = ['Hammad', 'Builder', 'Engine']

d = dict(zip(keys, values))

print(d) # {'Bob': 'Builder',

            'Safe': 'Hammad',

            'Thomas': 'Engine'}

# NOT SO GOOD

keys = ['Safe', 'Bob', 'Thomas']

values = ['Hammad', 'Builder', 'Engine']

d = {}

for i, key in enumerate(keys):

    d[keys] = values[i]

    print(d) # {'Bob': 'Builder',

                'Safe': 'Hammad',

                'Thomas': 'Engine'}

10. And the rest … !

● while True:

break # This will spark discussion!!!

● Generators and generator expressions.

● Avoid from module import *

Prefer: import numpy as np; import pandas as pd

● Use _ for “throwaway” variables e.g.:

for k, _ in [('a', 1), ('b', 2), ('c', 3)]

● dict.get() and dict.setdefault()

● collections.defaultdict

● Sort lists using l.sort(key=key_func)