python基本数据类型——str

Posted 2020-09-21

一、字符串的创建

test = str() / ""
test = str("licheng") / "licheng"

• 无参数，创建空字符串
• 一个参数，创建普通字符串
• 两个参数，int（字节，编码）

二、字符串的常用方法

#capitalize()：字符串首字符大写
string = ‘this is a string.‘
new_str = string.capitalize()
print(new_str)
#输出：This is a string.
 

#center(width, fillchar=None)：将字符串放在中间，在指定长度下，首尾以指定字符填充
string = ‘this is a string.‘
new_str = string.center(30,‘*‘)
print(new_str)
#输出：******this is a string.*******
 

#count(sub, start=None, end=None)：计算字符串中某字符的数量
string = ‘this is a string.‘
new_str = string.count(‘i‘)
print(new_str)
#输出：3
 

#decode/encode(encoding=None, errors=None)：解码/解码
string = ‘this is a string.‘
new_str = string.decode()
new_str = string.encode()
print(new_str)
 

#endswith(self, suffix, start=None, end=None)：判断是否以某字符结尾
string = ‘this is a string.‘
new_str = string.endswith(‘ing.‘)
print(new_str)
#输出：True
 

#find(self, sub, start=None, end=None)：在字符串中寻找指定字符的位置
string = ‘this is a string.‘
new_str = string.find(‘a‘) #找的到的情况
print(new_str)
#输出：8
new_str = string.find(‘xx‘) #找不到的情况返回-1
print(new_str)
#输出：-1
 

#index(self, sub, start=None, end=None)：；类似find
string = ‘this is a string.‘
new_str = string.index(‘a‘) #找的到的情况
print(new_str)
#输出：8
new_str = string.index(‘xx‘) #找不到的情况，程序报错
print(new_str)
#输出：程序运行报错，ValueError: substring not found

 

#isalnum(self)：判断字符串中是否都是数字和字母，如果是则返回True，否则返回False
string = ‘My name is yue,my age is 18.‘
new_str = string.isalnum()
print(new_str)
#输出：False
string = ‘haha18121314lala‘
new_str = string.isalnum()
print(new_str)
#输出：True
 

#isalpha(self)：判断字符串中是否都是字母，如果是则返回True，否则返回False
string = ‘abcdefg‘
new_str = string.isalpha()
print(new_str)
#输出：True
string = ‘my name is yue‘
new_str = string.isalpha() #字母中间带空格、特殊字符都不行
print(new_str)
#输出：False
 

# isdigit(self)：判断字符串中是否都是数字，如果是则返回True，否则返回False
string = ‘1234567890‘
new_str = string.isdigit()
print(new_str)
#输出：True
string = ‘haha123lala‘
new_str = string.isdigit() #中间带空格、特殊字符都不行
print(new_str)
#输出：False

 

# islower(self)：判断字符串中的字母是否都是小写，如果是则返回True，否则返回False
string = ‘my name is yue,my age is 18.‘
new_str = string.islower()
print(new_str)
#输出：True
string = ‘My name is Yue,my age is 18.‘
new_str = string.islower()
print(new_str)
#输出：False
 

# isupper(self)：检测字符串中所有的字母是否都为大写。
string = ‘MY NAME IS YUE.‘
new_str = string.isupper()
print(new_str)
#输出：True
string = ‘My name is Yue.‘
new_str = string.isupper()
print(new_str)
#输出：False

 

# join(self, iterable)：将序列中的元素以指定的字符连接生成一个新的字符串。
string = ("haha","lala","ohoh")
str = "-"
print(str.join(string))
#输出：haha-lala-ohoh
 

# lower(self)：转换字符串中所有大写字符为小写。
string = "My Name is YUE."
print(string.lower())
# 输出：my name is yue.

 

# lstrip(self, chars=None)：截掉字符串左边的空格或指定字符。
string = " My Name is YUE."
print(string.lstrip())
#输出：My Name is YUE.
string = "My Name is YUE."
print(string.lstrip(‘My‘))
#输出： Name is YUE.

 

#replace(self, old, new, count=None)：把字符串中的 old（旧字符串） 替换成 new(新字符串)，如果指定第三个参数max，则替换不超过 max 次。
string = "My name is yue."
print(string.replace("yue","ying"))
#输出：My name is ying.

 

# rfind(self, sub, start=None, end=None)：返回字符串最后一次出现的位置，如果没有匹配项则返回-1。
string = "My name is yue."
print(string.rfind(‘is‘))
#输出：8
string = "My name is yue."
print(string.rfind(‘XXX‘))
#输出：-1
 

# split(self, sep=None, maxsplit=None)：通过指定分隔符对字符串进行切片。
string = "haha lala gege"
print(string.split(‘ ‘))
#输出：[‘haha‘, ‘lala‘, ‘gege‘]
print(string.split(‘ ‘, 1 ))
#输出： [‘haha‘, ‘lala gege‘]

 

# rsplit(self, sep=None, maxsplit=None)：通过指定分隔符对字符串从右进行切片。
string = "haha lala gege"
print(string.rsplit(‘ ‘))
#输出：[‘haha‘, ‘lala‘, ‘gege‘]
print(string.rsplit(‘ ‘, 1 ))
#输出： [‘haha lala‘, ‘gege‘]

 

# rstrip(self, chars=None)：删除 string 字符串末尾的指定字符（默认为空格）.
string = " My name is yue. "
print(string.rstrip())
#输出： My name is yue.

 

# strip(self, chars=None)：移除字符串头尾指定的字符（默认为空格）。
string = " My name is yue. "
print(string.strip())
#输出：My name is yue.

 

# upper(self)：将字符串中的小写字母转为大写字母。
string = "my name is yue,my age is 18."
print(string.upper())
#输出：MY NAME IS YUE,MY AGE IS 18.

 str源码

三、字符串的公共功能

• 索引（只能取一个元素）
• 切片（取多个元素）
• 长度（len）
  • python2：按字节算长度
  • python3：按字符算长度
• for循环（同长度的版本循环单位）

四、字符与字节的转换

# 将gbk编码的字符转化为字节
s = "李程"
b = bytes(s, encoding="gbk")
type(b)  输出为字节类型

# 将字节转化为字符
c = str(b, encoding="gbk")

五、字符串格式化

Python的字符串格式化有两种方式: 百分号方式、format方式

百分号的方式相对来说比较老，而format方式则是比较先进的方式，企图替换古老的方式，目前两者并存。

1、百分号方式

%[(name)][flags][width].[precision]typecode

 参数详解

常用格式化：

tpl = "i am %s" % "spark"
 
tpl = "i am %s age %d" % ("spark", 18)
 
tpl = "i am %(name)s age %(age)d" % {"name": "spark", "age": 18}
 
tpl = "percent %.2f" % 99.97623
 
tpl = "i am %(pp).2f" % {"pp": 123.425556, }
 
tpl = "i am %.2f %%" % {"pp": 123.425556, }

2、Format方式

[[fill]align][sign][#][0][width][,][.precision][type]

 参数详解

 常用格式化：

 1 tpl = "i am {}, age {}, {}".format("seven", 18, ‘alex‘)
 2   
 3 tpl = "i am {}, age {}, {}".format(*["seven", 18, ‘alex‘])
 4   
 5 tpl = "i am {0}, age {1}, really {0}".format("seven", 18)
 6   
 7 tpl = "i am {0}, age {1}, really {0}".format(*["seven", 18])
 8   
 9 tpl = "i am {name}, age {age}, really {name}".format(name="seven", age=18)
10   
11 tpl = "i am {name}, age {age}, really {name}".format(**{"name": "seven", "age": 18})
12   
13 tpl = "i am {0[0]}, age {0[1]}, really {0[2]}".format([1, 2, 3], [11, 22, 33])
14   
15 tpl = "i am {:s}, age {:d}, money {:f}".format("seven", 18, 88888.1)
16   
17 tpl = "i am {:s}, age {:d}".format(*["seven", 18])
18   
19 tpl = "i am {name:s}, age {age:d}".format(name="seven", age=18)
20   
21 tpl = "i am {name:s}, age {age:d}".format(**{"name": "seven", "age": 18})
22  
23 tpl = "numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)
24  
25 tpl = "numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)
26  
27 tpl = "numbers: {0:b},{0:o},{0:d},{0:x},{0:X}, {0:%}".format(15)
28  
29 tpl = "numbers: {num:b},{num:o},{num:d},{num:x},{num:X}, {num:%}".format(num=15)

更多格式化操作：https://docs.python.org/3/library/string.html