python字符串格式化方式解析

1.%格式符

name = '李四'
age = 18
a = "姓名:%s,年龄:%s"%(name,age)
print(a)   #姓名:李四,年龄:18
​
b = "%(name)s,%(age)s"%{'name':'张三','age':18}
print(b)   #张三,18

这种格式化并不是很好，因为它很冗长并且容易导致错误，比如没有正确显示元组或字典

2.str.format()

name = '李四'
age = 18
# 替换字段用大括号进行标记
a1 = "hello, {}. you are {}?".format(name,age)
print(a1)   #hello, 李四. you are 18?
​
# 通过索引来以其他顺序引用变量
a2 = "hello, {1}. you are {0}?".format(age,name)
print(a2)  #hello, 李四. you are 18?
​
# 通过参数来以其他顺序引用变量
a3 = "hello, {name}. you are {age1}?".format(age1=age,name=name)
print(a3)  #hello, 李四. you are 18?
​
# 从字典中读取数据时还可以使用 **
data = {"name":"张三","age":18}
a4 = "hello, {name}. you are {age}?".format(**data)
print(a4)  #hello, 李四. you are 18?

在处理多个参数和更长的字符串时仍然可能非常冗长

3.f-Strings

f-strings 是指以 f 或 F 开头的字符串，其中以 {} 包含的表达式会进行值替换。

name = '李四'
age = 18
# F 和 f 的简单使用
b1 = f"hello, {name}. you are {age}?"
b2 = F"hello, {name}. you are {age}?"
print(b1)   # hello, 李四. you are 18?
print(b2)   # hello, 李四. you are 18?

# 字典也可以
teacher = {'name': 'meet', 'age': 18}
msg = f"The teacher is {teacher['name']}, aged {teacher['age']}"
print(msg) # The comedian is meet, aged 18

# 列表也行
l1 = ['meet', 18]
msg = f'姓名：{l1[0]},年龄：{l1[1]}.'
print(msg) # 姓名：meet,年龄：18.

#可以插入表达式
def sum_a_b(a,b):
  return a + b
a = 1
b = 2
print('求和的结果为' + f'{sum_a_b(a,b)}')

#多行f 反斜杠
name = 'barry'
age = 18
ajd = 'handsome'

speaker = f'Hi {name}.'\
     f'You are {age} years old.'\
     f'You are a {ajd} guy!'
print(speaker)  #Hi barry.You are 18 years old.You are a handsome guy!
print(f"{You are very \"handsome\"}")   #报错


#括号的处理 -->重点：两对为一组
print(f"{{73}}") # {73}
print(f"{{{73}}}") # {73}
print(f"{{{{73}}}}") # {{73}}


m = 21
# ! , : { } ;这些标点不能出现在{} 这里面。
# print(f'{;12}') # 报错
# 所以使用lambda 表达式会出现一些问题。
# 解决方式：可将lambda嵌套在圆括号里面解决此问题。
x = 5
print(f'{(lambda x: x*2) (x)}') # 10

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