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一、舊式的字符串格式化
% 操作符
參考以下示例：
>>> name = "Eric" >>> "Hello, %s." % name 'Hello, Eric.'
當有多個變量需要插入到字符串中時：
>>> name = "Eric" >>> age = 74 >>> "Hello, %s. You are %s." % (name, age) 'Hello, Eric. You are 74.'
當需要替換的變量進一步增多時，使用 % 操作符格式化字符串會導致代碼可讀性變得很差：
>>> 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() 是對 % 方式的改進，它使用常見的函數調用的語法，并且可以通過定義對象本身的 __format__() 方法控制字符串格式化的具體行為。
基本用法：
>>> name = "Eric"
>>> age = 74
>>> "Hello, {}. You are {}.".format(name, age)
'Hello, Eric. You are 74.'
str.format() 相對于 % 操作符有著更強的靈活性。比如可以通過數字索引來關聯替換到字符串中的變量：
>>> name = "Eric"
>>> age = 74
>>> "Hello, {1}. You are {0}.".format(age, name)
'Hello, Eric. You are 74.'
為了提高代碼可讀性， {} 中也可以使用有具體含義的參數名：
>>> name = "Eric"
>>> age = 74
>>> "Hello, {name}. You are {age}".format(name=name, age=age)
'Hello, Eric. You are 74'
針對字典結構的數據：
>>> person = {'name': 'Eric', 'age': 74}
>>> "Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])
'Hello, Eric. You are 74.'
或者更簡潔的方式：
>>> person = {'name': 'Eric', 'age': 74}
>>> "Hello, {name}. You are {age}.".format(**person)
'Hello, Eric. You are 74.'
問題在于當需要替換的變量很多時， str.format() 方式依然會導致代碼變得過于冗長：
>>> 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.'
嵌入表達式
>>> 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 中還可以直接嵌入某個對象實例，只要其內部實現了 __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.'
總結
以上所述是小編給大家介紹的Python3 中的字符串格式化語法，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對億速云網站的支持！
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