Python字符串格式化实例讲解

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:

'''
学习中遇到问题没人解答？小编创建了一个Python学习交流群：711312441
寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！
'''
%%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}}'

到此这篇关于Python字符串格式化实例讲解的文章就介绍到这了,更多相关Python字符串内容请搜索猪先飞以前的文章或继续浏览下面的相关文章希望大家以后多多支持猪先飞！