几个有用的python字符串函数(format,join,split,startwith,endwith,lower,upper)

你需要知道的python字符串函数

format

字符串的format函数为非字符串对象嵌入字符串提供了一种非常强大的方法。在format方法中，字符串使用{}来代替一系列字符串的参数并规定格式。下面通过几个例子来详细解释其用法

直接使用{}

apple_num = 10
print("I have {} apples".format(apple_num))

在{}中使用位置参数1

nums = [4, 5, 6]
msg = "Numbers: {0} {1} {0}".format(nums[0], nums[1])
print(msg)
# Numbers: 4 5 4

在{}中使用位置参数2

msg = "Numbers: {a} {c} {b}".format(a=5, b=6, c=7)
print(msg)
# Numbers: 5 7 6

{}中的更多格式

_ = [print("{}x{}={:<4}".format(y, x, x*y), end="\n" if x==y else "") for x in range(1, 10) for y in range(1, x+1)]

:<4表示左对齐占用四格位置，其结果为：

1x1=1
1x2=2 2x2=4
1x3=3 2x3=6 3x3=9
1x4=4 2x4=8 3x4=12 4x4=16
1x5=5 2x5=10 3x5=15 4x5=20 5x5=25
1x6=6 2x6=12 3x6=18 4x6=24 5x6=30 6x6=36
1x7=7 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=49
1x8=8 2x8=16 3x8=24 4x8=32 5x8=40 6x8=48 7x8=56 8x8=64
1x9=9 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81

join()

joins a list of strings with another string as a separator

print(", ".join(["spam", "eggs", "ham"]))
# spam, eggs, ham

更多见避免使用“+”操作符在python中连接字符串

split

join的逆向

print("spam, eggs, ham".split(", "))
# ['spam', 'eggs', 'ham']

replace()

replaces one substring in a string with another

print("Hello ME".replace("ME", "world")
# Hello world

startwith, endwith

determine if there is a substring at the start and end of a string, respectively.

print("This is a sentence".startwith("This"))
# True
print("This is a sentence".endwith("sentence"))
# False

lower, upper

change the case of a string

print("hello world".upper())
# HELLO WORLD
print("HELLO WORLD".lower())
# hello world