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)