一、舊式的字串格式化
% 操作符
參考以下示例：
>>> name = "eric"
>>> "hello, %s." % name
'hel程式設計客棧lo, eric.'
當有多個變數需要插入到字串中時：
>>> name = "eric"
>&nsueqgt;> 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**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, age)
'hello, 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, . you are .".format(age, name)
'hello, eric. you are 74.'
為了提高**可讀性， {} 中也可以使用有具體含義的引數名：
>>> name = "eric"
>>> age = 74
>>> "hello, . you are ".format(name=name, age=age)
'hello, eric. you are 74'
針對字典結構的資料：
>>> person =
>>> "hello, . you are .".format(name=person['name'], age=person['age'])
'hello, eric. you are 74.'
或者更簡潔的方式：
>>> person =
>>> "hello, . you are .".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**變得過於冗長：
>>> first_name = "eric"
>>> last_name = "idle"
>>> age = 74
>>> profession = "comedian"
>>> affiliation = "monty python"
>>> "hello, . you are . \
you are a . you were a member of ."\
.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"
>&程式設計客棧gt;> age = 74
>>> f"hello, . you are ."
'hello, eric. you are 74.'
嵌入表示式
>>> f""
'74'
>>> def to_lowercase(input):
... return input.lower()
>>> name = "eric idle"
>>> f" is funny"
'eric idle is funny'
>>> f" 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, last_name, age):
self.first_name = first_name
self.last_name = last_name
self.age = age
def __str__(self):
return f" is "
new_comedian = comedian("eric", "idle", 74)
print(f"")
# eric idle is 74
多行 f-string
>>> name = "eric"
>>> profession = www.cppcns.com"comedian"
>>> affiliation = "monty pythnsueqon"
>>> message = (
... f"hi . "
... f"you are a . "
... f"you were in ."
... )
>>> message
'hi eric. you are a comedian. you were in monty python.'
總結本文標題: 詳解python3 中的字串格式化語法
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