一、旧式的字符串格式化

% 操作符

参考以下示例：

>>> name = "Eric">>> "Hello, %s." % name'Hello, Eric.'

当有多个变量需要插入到字符串中时：

>>> name = "Eric">>> age = 74>>> "Hello, %s. You are %s." % (name, age)'Hello, Eric. You are 74.'

当需要替换的变量进一步增多时，使用 % 操作符格式化字符串会导致代码可读性变得很差：

>>> first_name = "Eric">>> last_name = "Idle">>> age = 74>>> profession = "comedian">>> affiliation = "Monty Python">>> "Hello, %s %s. You are %s. You are a %s. You were a member of %s." % (first_name, last_name, age, profession, affiliation)'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

str.format()

str.format() 是对 % 方式的改进，它使用常见的函数调用的语法，并且可以通过定义对象本身的 __format__() 方法控制字符串格式化的具体行为。

基本用法：

>>> name = "Eric">>> age = 74>>> "Hello, {}. You are {}.".format(name, age)'Hello, Eric. You are 74.'

str.format() 相对于 % 操作符有着更强的灵活性。比如可以通过数字索引来关联替换到字符串中的变量：

>>> name = "Eric">>> age = 74>>> "Hello, {1}. You are {0}.".format(age, name)'Hello, Eric. You are 74.'

为了提高代码可读性，{} 中也可以使用有具体含义的参数名：

>>> name = "Eric">>> age = 74>>> "Hello, {name}. You are {age}".format(name=name, age=age)'Hello, Eric. You are 74'

针对字典结构的数据：

>>> person = {'name': 'Eric', 'age': 74}>>> "Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])'Hello, Eric. You are 74.'

或者更简洁的方式：

>>> person = {'name': 'Eric', 'age': 74}>>> "Hello, {name}. You are {age}.".format(**person)'Hello, Eric. You are 74.'

问题在于当需要替换的变量很多时，str.format() 方式依然会导致代码变得过于冗长：

>>> first_name = "Eric">>> last_name = "Idle">>> age = 74>>> profession = "comedian">>> affiliation = "Monty Python">>> "Hello, {first_name} {last_name}. You are {age}. \ You are a {profession}. You were a member of {affiliation}."\ .format(first_name=first_name, last_name=last_name, age=age, \ profession=profession, affiliation=affiliation)'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

二、f-string

基本用法

>>> name = "Eric">>> age = 74>>> f"Hello, {name}. You are {age}."'Hello, Eric. You are 74.'

嵌入表达式

>>> f"{2 * 37}"'74'>>> def to_lowercase(input):... return input.lower() >>> name = "Eric Idle">>> f"{to_lowercase(name)} is funny"'eric idle is funny'>>> f"{name.lower()} is funny"'eric idle is funny'

f-string 中还可以直接嵌入某个对象实例，只要其内部实现了 __str__ 或者 __repr__ 方法：

class Comedian: def __init__(self, first_name, last_name, age): self.first_name = first_name self.last_name = last_name self.age = age def __str__(self): return f"{self.first_name} {self.last_name} is {self.age}"new_comedian = Comedian("Eric", "Idle", 74)print(f"{new_comedian}")# Eric Idle is 74

多行 f-string

>>> name = "Eric">>> profession = "comedian">>> affiliation = "Monty Python">>> message = (... f"Hi {name}. "... f"You are a {profession}. "... f"You were in {affiliation}."... )>>> message'Hi Eric. You are a comedian. You were in Monty Python.'

参考资料

Python 3's f-Strings: An Improved String Formatting Syntax (Guide)

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