Python字符串格式化实例讲解
作者：Python热爱者
在Python 3.6之前，有两种将Python表达式嵌入到字符串文本中进行格式化的主要方法：％-formatting和str.format（）
一、%-formatting
name = "Eric" age = 74 "Hello, %s. You are %s." % (name, age)
注：这种格式不是很好，因为它是冗长的，会导致错误。
二、str.format（）
str.format() 在Python 2.6中引入的。
（1）使用str.format（），替换字段用大括号标记：
"Hello, {}. You are {}.".format(name, age)# 输出结果：'Hello, Eric. You are 74.'
（2）可以通过引用其索引来以任何顺序引用变量：
"Hello, {1}. You are {0}-{0}.".format(age, name)# 输出结果：'Hello, Eric. You are 74-74.'
（3）如果插入变量名称，则会获得额外的能够传递对象的权限，然后在大括号之间引用参数和方法：
person = {'name': 'Eric', 'age': 74}
"Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])
# 输出结果：'Hello, Eric. You are 74.'
（4）可以使用**来用字典来完成这个巧妙的技巧：
person = {'name': 'Eric', 'age': 74}
"Hello, {name}. You are {age}.".format(**person)
# 输出结果：'Hello, Eric. You are 74.'
注：当处理多个参数和更长的字符串时，str.format()仍然可能非常冗长。
三、f-Strings
f-Strings是在Python 3.6开始加入标准库。也称为“格式化字符串文字”，F字符串是开头有一个f的字符串文字，以及包含表达式的大括号将被其值替换。
（1）f-Strings
name = "Eric"
age = 74
f"Hello, {name}. You are {age}."
# 输出结果：'Hello, Eric. You are 74.'
（2）用大写字母F也是有效的：
name = "Eric"
age = 74
F"Hello, {name}. You are {age}."
# 输出结果：'Hello, Eric. You are 74.'
（3）可以调用函数
name = "Eric"
age = 74
f"{name.lower()} is funny."
# 输出结果：'eric is funny.'
f"{2 * 37}"
# 输出结果：'74'
（4）可以使用带有f字符串的类创建对象
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}."
def __repr__(self):
return f"{self.first_name} {self.last_name} is {self.age}. Surprise!"
new_comedian = Comedian("Eric", "Idle", "74")
f"{new_comedian}"
# 输出结果;'Eric Idle is 74.'
f"{new_comedian!r}"
# 输出结果：'Eric Idle is 74. Surprise!'
（5）多行f-string
message = (f"Hi {name}. "
f"You are a {profession}. "
f"You were in {affiliation}.")# 输出结果：'Hi Eric. You are a comedian. You were in Monty Python.'
message = (f"Hi {name}. "
"You are a {profession}. "
"You were in {affiliation}.")
# 输出结果：'Hi Eric. You are a {profession}. You were in {affiliation}.'
（6）使用"“”
message = f"""
Hi {name}.
You are a {profession}.
You were in {affiliation}.
"""# 输出结果：'\n Hi Eric. \n You are a comedian. \n You were in Monty Python.\n '
（7）性能
f字符串中的f也可以代表“速度快”。f-字符串是运行时渲染的表达式，而不是常量值。
速度比较:
'''
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'''
%%timeit
name = "Eric"
age = 74
'%s is %s.' % (name, age)
# 202 ns ± 2.05 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%%timeit
name = "Eric"
age = 74
'{} is {}.'.format(name, age)
# 244 ns ± 5.52 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%%timeit
name = "Eric"
age = 74
'{name} is {age}.'
# 14.4 ns ± 0.0121 ns per loop (mean ± std. dev. of 7 runs, 100000000 loops each)（8）语法正确格式
f"{'Eric Idle'}"
# 输出结果：'Eric Idle'
f'{"Eric Idle"}'
# 输出结果：'Eric Idle'
f"""Eric Idle"""
# 输出结果：'Eric Idle'
f'''Eric Idle'''
# 输出结果：'Eric Idle'
f"The \"comedian<span class="string">" is {name}, aged {age}."
# 输出结果：'The "comedian" is Eric, aged 74.'
（9）字典
字典的键使用单引号，请记住确保对包含键的f字符串使用双引号。
comedian = {'name': 'Eric Idle', 'age': 74}
f"The comedian is {comedian['name']}, aged {comedian['age']}."
# 输出结果：'The comedian is Eric Idle, aged 74.'
（10）大括号
为了使字符串出现大括号，您必须使用双大括号：
f"{{74}}"
# 输出结果：'{74}'
f"{{{{74}}}}"
# 输出结果：'{{74}}'
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