Python 中 f-Strings 的作用

str_value = "hello，python coders" 
print(f"{ str_value = }") 
# str_value = 'hello，python coders' 

num_value = 123 
print(f"{num_value % 2 = }") 
# num_value % 2 = 1 

import datetime 
 
today = datetime.date.today() 
print(f"{today: %Y%m%d}") 
# 20211019 
print(f"{today =: %Y%m%d}") 
# today = 20211019 

>>> a = 42 
>>> f"{a:b}" # 2进制 
'101010' 
>>> f"{a:o}" # 8进制 
'52' 
>>> f"{a:x}" # 16进制，小写字母 
'2a' 
>>> f"{a:X}" # 16进制，大写字母 
'2A' 
>>> f"{a:c}" # ascii 码 
'*' 

>>> num_value = 123.456 
>>> f'{num_value = :.2f}' #保留 2 位小数 
'num_value = 123.46' 
>>> nested_format = ".2f" #可以作为变量 
>>> print(f'{num_value:{nested_format}}') 
123.46 

>>> x = 'test' 
>>> f'{x:>10}'# 右对齐，左边补空格 
'test' 
>>> f'{x:*<10}'  # 左对齐，右边补* 
'test******' 
>>> f'{x:=^10}'  # 居中，左右补= 
'===test===' 
>>> x, n = 'test', 10 
>>> f'{x:~^{n}}' # 可以传入变量 n 
'~~~test~~~' 
>>> 

>>> x = '中' 
>>> f"{x!s}" # 相当于 str(x) 
'中' 
>>> f"{x!r}" # 相当于 repr(x) 
"'中'" 

class MyClass: 
 def __format__(self, format_spec) -> str: 
  print(f'MyClass __format__ called with {format_spec=!r}') 
  return "MyClass()" 
 
 
print(f'{MyClass():bala bala  %%MYFORMAT%%}') 

MyClass __format__ called with format_spec='bala bala  %%MYFORMAT%%' 
MyClass()