一、舊式的字串格式化

% 操作符

參考以下示例：

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

當有多個變數需要插入到字串中時：

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

當需要替換的變數進一步增多時，使用 % 操作符格式化字串會導致程式碼可讀性變得很差：

>>> 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，它使用常見的函式呼叫的語法，並且可以通過定義物件本身的 __format__() 方法控制字串格式化的具體行為。

基本用法：

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

str.format() 相對於 % 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串中的變數：

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

為了提高程式碼可讀性，{} 中也可以使用有具體含義的引數名：

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

針對字典結構的資料：

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

問題在於當需要替換的變數很多時，str.format() 方式依然會導致程式碼變得過於冗長：

>>> 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.'

嵌入表示式

>>> 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物件例項，只要其內部實現了 __str__ 或者 __repr__ 方法：

class Comedian:
  def __init__(self,first_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.'

參考資料

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

以上就是python 字串格式化的示例的詳細內容，更多關於python 字串格式化的資料請關注我們其它相關文章！