Python编程惯例
- 为什么要关心Python编程惯例？因为能让你的代码更加Pythonic！
1. 让代码既能当模块被import又能直接执行
if __name__ = '__main__':
2. 用下面的方式判断逻辑 "真"或"假"
if x:
if not x:
name = 'Qiangsheng He'
fruits = ['apple', 'orange']
scores = {'Jim': 88, 'Mary': 78}
# GOOD
if name and fruits and scores:
print(True)
# NOT SO GOOD
if name != '' and fruits != [] and scores != {}:
print(True)
- What's is Truth?
| True | False |
|---|---|
| 非空字符串 | 空字符串 |
| 非0数字 | 数字0 |
| 非空的container：len(x) > 0 | 空的container：len(x) == 0 |
| - | None |
| 布尔True | 布尔False |
| nonzero (2.x) / bool (3.x) | nonzero (2.x) / bool (3.x) |
3. 善用in运算符
if x in items: # Contains
for x in items: # Iteration
title = 'Python idioms'
# GOOD
if 'd' in title:
print('Title contains char d')
# NOT SO GOOD
if title.find('d') != -1:
print('Title not contains char d')
names = ['Jim', 'Mary']
# GOOD
for name in names:
print(name)
# NOT SO GOOD
i = 0
while i < len(names):
print(names[i])
4. 不借用临时变量交换值
a, b = 'Jim', 'Mary'
# GOOD
a, b = b, a
# NOT SO GOOD
temp = a
a = b
b = a
5. 用sequence构建字符串
letters = ['J', 'o', 'h', 'n', 's', 'o', 'n']
# GOOD
name = ''.join(letters) # 时间复杂度O(n)
# NOT SO GOOD
name = ''
for letter in letters: # 时间复杂度O(n**2)
name += letter
6. EAFP is preferable to LBYL
- EAFP - Easier to Ask Forgiveness than Permission.
- LBYL - Look Before You Leap.
# Python中抛出异常的代价不像其他语言那么大
try: v. if ...: except:
scores = {'Jim': '87'}
# GOOD
try:
score = int(scores['Jim'])
except (KeyError, TypeError, ValueError):
score = None
# NOT SO GOOD
if 'Jim' in scores and isinstance(scores['Jim'], str)
and scores['Jim'].isdigit():
score = int(scores['Jim'])
else:
score = None
7. 使用enumerate
names = ['Jim', 'Mary', 'Tom']
# GOOD
for i, name in enumerate(names):
print(i, name)
# NOT SO GOOD
i = 0
for name in names:
print(i, name)
i += 1
8. 用列表推导式式构建lists
nums = list(range(10))
# GOOD
odd_nums = [x for x in nums if x % 2 == 1]
# NOT SO GOOD
odd_nums = []
for num in nums:
if num % 2 == 1:
odd_nums.append(num)
9. 通过zip函数组合键和值构建字典
# d = dict(zip(keys, values))
students = ['Jim', 'Mary', 'Tom']
scores = [89, 34, 56]
# GOOD
student_scores = dict(zip(students, scores))
# NOT SO GOOD
student_scores = []
for i, name in enumerate(students):
student_scores[name] = scores[i]
10. 其他
使用Generators（生成器） and generator expressions
避免使用 from module import *
好的写法: import numpy as np; import pandas as pd使用 _ 作为一次性变量 e.g.:
for k, _ in [('a', 1), ('b', 2), ('c', 3)]dict.get() and dict.setdefault()
collections.defaultdict
用 l.sort(key=key_func)进行列表排序
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祝生活愉快！