182 lines
3.7 KiB
Markdown
182 lines
3.7 KiB
Markdown
## Python惯例
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“惯例”这个词指的是“习惯的做法，常规的办法，一贯的做法”，与这个词对应的英文单词叫“idiom”。由于Python跟其他很多编程语言在语法和使用上还是有比较显著的差别，因此作为一个Python开发者如果不能掌握这些惯例，就无法写出“Pythonic”的代码。下面我们总结了一些在Python开发中的惯用的代码。
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1. 让代码既可以被导入又可以被执行。
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```Python
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if __name__ == '__main__':
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```
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2. 用下面的方式判断逻辑“真”或“假”。
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```Python
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if x:
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if not x:
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```
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**好**的代码：
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```Python
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name = 'jackfrued'
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fruits = ['apple', 'orange', 'grape']
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owners = {'1001': '骆昊', '1002': '王大锤'}
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if name and fruits and owners:
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print('I love fruits!')
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```
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**不好**的代码：
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```Python
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name = 'jackfrued'
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fruits = ['apple', 'orange', 'grape']
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owners = {'1001': '骆昊', '1002': '王大锤'}
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if name != '' and len(fruits) > 0 and owners != {}:
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print('I love fruits!')
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```
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3. 善于使用in运算符。
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```Python
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if x in items: # 包含
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for x in items: # 迭代
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```
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**好**的代码：
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```Python
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name = 'Hao LUO'
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if 'L' in name:
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print('The name has an L in it.')
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```
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**不好**的代码：
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```Python
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name = 'Hao LUO'
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if name.find('L') != -1:
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print('This name has an L in it!')
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```
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4. 不使用临时变量交换两个值。
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```Python
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a, b = b, a
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```
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5. 用序列构建字符串。
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**好**的代码：
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```Python
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chars = ['j', 'a', 'c', 'k', 'f', 'r', 'u', 'e', 'd']
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name = ''.join(chars)
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print(name) # jackfrued
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```
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**不好**的代码：
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```Python
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chars = ['j', 'a', 'c', 'k', 'f', 'r', 'u', 'e', 'd']
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name = ''
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for char in chars:
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name += char
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print(name) # jackfrued
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```
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6. EAFP优于LBYL。
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EAFP - **E**asier to **A**sk **F**orgiveness than **P**ermission.
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LBYL - **L**ook **B**efore **Y**ou **L**eap.
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**好**的代码：
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```Python
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d = {'x': '5'}
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try:
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value = int(d['x'])
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print(value)
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except (KeyError, TypeError, ValueError):
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value = None
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```
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**不好**的代码：
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```Python
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d = {'x': '5'}
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if 'x' in d and isinstance(d['x'], str) \
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and d['x'].isdigit():
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value = int(d['x'])
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print(value)
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else:
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value = None
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```
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7. 使用enumerate进行迭代。
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**好**的代码：
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```Python
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fruits = ['orange', 'grape', 'pitaya', 'blueberry']
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for index, fruit in enumerate(fruits):
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print(index, ':', fruit)
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```
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**不好**的代码：
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```Python
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fruits = ['orange', 'grape', 'pitaya', 'blueberry']
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index = 0
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for fruit in fruits:
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print(index, ':', fruit)
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index += 1
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```
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8. 用生成式生成列表。
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**好**的代码：
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```Python
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data = [7, 20, 3, 15, 11]
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result = [num * 3 for num in data if num > 10]
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print(result) # [60, 45, 33]
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```
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**不好**的代码：
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```Python
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data = [7, 20, 3, 15, 11]
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result = []
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for i in data:
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if i > 10:
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result.append(i * 3)
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print(result) # [60, 45, 33]
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```
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9. 用zip组合键和值来创建字典。
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**好**的代码：
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```Python
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keys = ['1001', '1002', '1003']
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values = ['骆昊', '王大锤', '白元芳']
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d = dict(zip(keys, values))
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print(d)
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```
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**不好**的代码：
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```Python
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keys = ['1001', '1002', '1003']
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values = ['骆昊', '王大锤', '白元芳']
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d = {}
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for i, key in enumerate(keys):
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d[key] = values[i]
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print(d)
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```
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> **说明**：这篇文章的内容来自于网络，有兴趣的读者可以阅读[原文](http://safehammad.com/downloads/python-idioms-2014-01-16.pdf)。
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