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詳解Python3 中的字符串格式化語法

更新時(shí)間：2020年01月15日 08:33:37 投稿：mrr

字符串的格式化方法分為兩種，分別為占位符(%)和format方式。這篇文章主要介紹了Python3 中的字符串格式化語法問題,需要的朋友可以參考下

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(dāng)有多個(gè)變量需要插入到字符串中時(shí)：

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

當(dāng)需要替換的變量進(jìn)一步增多時(shí)，使用 % 操作符格式化字符串會導(dǎo)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(jìn)，它使用常見的函數(shù)調(diào)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(qiáng)的靈活性。比如可以通過數(shù)字索引來關(guān)聯(lián)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(shù)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(jié)構(gòu)的數(shù)據(jù)：

>>> 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(dāng)需要替換的變量很多時(shí)， str.format() 方式依然會導(dǎo)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(dá)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(gè)對象實(shí)例，只要其內(nèi)部實(shí)現(xiàn)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(jié)

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(shí)回復(fù)大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！
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