原文, 知乎 - 刘哈哈

使用方法

字符串

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>>> name = 'Python'
>>> age = 18
>>> f"hi, {name}, are you {age}"
'hi, Python, are you 18'
>>> F"hi, {name}, are you {age}"
'hi, Python, are you 18'

运算

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>>> f"{ 2 * 3 + 1}"
'7'

函数

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>>> def test(input):
... return input.lower()
...
>>> name = "Python"
>>> f"{test(name)} is handsome."
'python is handsome.'
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>>> f"{name.lower()} is handsome."
'python is handsome.'

在类中使用

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>>> class Person:
... def __init__(self,name,age):
... self.name = name
... self.age = age
... def __str__(self):
... return f"{self.name} is {self.age}"
... def __repr__(self):
... return f"{self.name} is {self.age}. HAHA!"
...
>>> Python = Person("Python",18)
>>> f"{Python}"
'Python is 18'
>>> f"{Python!r}"
'Python is 18. HAHA!'
>>> print(Python)
Python is 18
>>> Python
Python is 18. HAHA!

多行

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>>> name = 'Python'
>>> age = 18
>>> message = {
... f'hi {name}.'
... f'you are {age}.'
... }
>>>
>>> message
{'hi Python.you are 18.'}

这里需要注意,每行都要加上 f 前缀,否则格式化会不起作用:

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>>> message = {
... f'hi {name}.'
... 'you are learning {status}.'
... }
>>> message
{'hi Python.you are learning {status}.'}

速度对比

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from timeit import timeit

print(timeit("""name = "Python"
age = 18
'%s is %s.' % (name, age)""", number = 10000))

print(timeit("""name = "Python"
age = 18
'{} is {}.'.format(name, age)""", number = 10000))

print(timeit("""name = "Python"
age = 18
f'{name} is {age}.'""", number = 10000))

结果

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$ python fstring.py
0.002238000015495345
0.004068000009283423
0.0015349999885074794

注意事项

可以在字符串中使用各种引号,只要保证和外部的引号不重复即可。

以下使用方式都是没问题的:

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>>> f"{'Python'}"
'Python'
>>> f'{"Python"}'
'Python'
>>> f"""Python"""
'Python'
>>> f'''Python'''
'Python'

那如果字符串内部的引号和外部的引号相同时呢?那就需要 \ 进行转义:

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>>> f"You are very \"handsome\""
'You are very "handsome"'
括号的处理
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>>> f"{{74}}"
'{74}'

>>> f"{{{74}}}"
'{74}'

可以看出,使用三个括号包裹效果一样。

反斜杠
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>>> f"You are very \"handsome\""
'You are very "handsome"'
>>> f"{You are very \"handsome\"}"
File "<stdin>", line 1
SyntaxError: f-string expression part cannot include a backslash

你可以先在变量里处理好待转义的字符,然后在表达式中引用变量:

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>>> name = '"handsome"'
>>> f'{name}'
'"handsome"'
注释符号
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>>> f"Python is handsome # really"
'Python is handsome # really'
>>> f"Python is handsome {#really}"
File "<stdin>", line 1
SyntaxError: f-string expression part cannot include '#'