原文，知乎 - 刘哈哈
使用方法
字符串
1
2
3
4
5
6
| >>> 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
1
2
| >>> f"{ 2 * 3 + 1}"
'7'
|
函数
1
2
3
4
5
6
| >>> def test(input):
... return input.lower()
...
>>> name = "Python"
>>> f"{test(name)} is handsome."
'python is handsome.'
|
1
2
| >>> f"{name.lower()} is handsome."
'python is handsome.'
|
在类中使用
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
| >>> 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
1
2
3
4
5
6
7
8
9
| >>> 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：
1
2
3
4
5
6
| >>> message = {
... f'hi {name}.'
... 'you are learning {status}.'
... }
>>> message
{'hi Python.you are learning {status}.'}
|
速度对比
1
2
3
4
5
6
7
8
9
10
11
12
13
| 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
1
2
3
4
| $ 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：
1
2
3
4
5
6
7
8
| >>> 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：
1
2
| >>> f"You are very \"handsome\""
'You are very "handsome"'
|
括号的处理
1
2
3
4
5
| >>> 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
1
2
3
4
5
| >>> 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：
1
2
3
| >>> name = '"handsome"'
>>> f'{name}'
'"handsome"'
|
注释符号
1
2
3
4
5
| >>> 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 '#'
|