A summary of common operations on python strings and a summary of python strings

A summary of common operations on python strings and a summary of python strings

This article provides examples of how to operate python strings for your reference. The specific content is as follows:

1. Remove Spaces
Str. strip ():Delete the specified characters on both sides of the string, and write the specified characters in parentheses. The default value is space.

>>> a=' hello '>>> b=a.strip()>>> print(b)hello

Str. lstrip ():Delete the specified character on the left of the string, and write the specified character into parentheses. The default character is space.

>>> A = 'hello' >>> B = a. lstrip () >>> print (B) hello # spaces on the right may not be obvious.

Str. rstrip ():Deletes the specified character on the right of the string. The default value is space.

>>> a=' hello '>>> b=a.rstrip()>>> print(b) hello

2. Copy the string

>>> a='hello world'>>> b=a>>> print(a,b)hello world hello world

3. connection string

+: Connect two strings >>> a = 'hello' >>>> B = 'World' >>> print (a + B) hello world note: this method is also called "the plus sign of all evil", because the static function string_concat (register PyStringObject * a, register PyObject * B) is called when two strings are connected using the plus sign ), in this function, we will open up a storage unit that is the sum of a + B memory, and then copy the and B strings. If n strings are connected, memory will be opened up for n-1 times, which is very resource-consuming. Str. join: connects two strings. You can specify the join symbol (for join, you can view related information on your own) >>> a = 'hello' >>> B = '####' >>>. join (B) '# hello #'

4. Search for strings

# The str. index and str. find functions are the same. The difference is that if the find () search fails,-1 is returned and the program running is not affected. Find is generally used! =-1 or find>-1 as the judgment condition. Str. index: Check whether the string contains a substring 'str'. The value range is a = 'Hello world' >>>. index ('l') 2>. index ('x') Traceback (most recent call last): File "<pyshell #40>", line 1, in <module>. index ('x') ValueError: substring not foundstr. find: Check whether the string contains the substring 'str'. You can specify the range >>> a = 'Hello world' >>>. find ('l') 2 >>>. find ('x')-1

5. compare strings

Str. cmp: Compares two objects and returns an integer based on the result. X <Y, the return value is negative, and X> Y returns a positive number.
# This method is not available in python3. this is written in the official documentation:
The cmp () function shocould be treated as gone, and the _ cmp _ () special method is no longer supported. use _ lt _ () for sorting, _ eq _ () with _ hash _ (), and other rich comparisons as needed. (If you really need the cmp () functionality, you cocould use the expression (a> B)-(a <B) as the equivalent for cmp (a, B ).)
The general idea is that the cmp () function has "Left". If you really need the cmp () function, you can use the expression (a> B)-(a <B) replace cmp (a, B)

>>> a=100>>> b=80>>> cmp(a,b)1

6. whether to include the specified string

in |not in >>> a='hello world'>>> 'hello' in aTrue>>> '123' not in aTrue

7. String Length

str.len>>> a='hello world'>>> print(len(a))11

8. Convert uppercase and lowercase letters in a string

S. lower () # convert to lowercase >>> a = 'Hello world' >>> print (. lower () hello worldS. upper () # convert to uppercase >>> a = 'Hello world' >>> print (. upper () hello worlds. swapcase () # case-insensitive swaps >>> a = 'Hello world' >>> print (. swapcase () hELLO wORLDS. capitalize () # uppercase letter >>> a = 'Hello world' >>> print (. capitalize () Hello world

9. You can specify the length and the two sides of the string in the center position.

str.center()>>> a='hello world'>>> print(a.center(40,'*'))**************hello world***************

10. String statistics

>>> a='hello world'>>> print(a.count('l'))3

11. Test and judge functions of strings. These functions are not in the string module. These functions return bool values.

S. startswith (prefix [, start [, end]) # whether to start with prefix S. endswith (suffix [, start [, end]) # end with suffix S. isalnum () # whether it is all letters and numbers with at least one character S. isalpha () # whether it is all letters with at least one character S. isdigit () # whether it is all numbers with at least one character S. isspace () # whether it is all blank characters with at least one character S. islower () # Whether the letters in S are all lowercase S. isupper () # Whether the letters in S are uppercase S. istitle () # whether S is capitalized

12. String Slicing

Str = '000000' print str [0: 3] # print str [:] # capture all characters of a string from the first to the third. print str [:] # print str [: -3] # print str [2] # capture the third character print str [-1] # capture the first character print str [:: -1] # create a print str [-3:-1] string that is in the opposite order of the original string # capture the print str [-3:] character before the last and last digits # intercept the last third digit to the End of print str [:-5:-3] # intercept the last fifth digit and the last third digit in reverse order

It should be emphasized that the string object cannot be changed. That is to say, after creating a string in python, you cannot change a part of the character. After any of the above functions change the string, a new string is returned, and the original string is not changed.

The above is all the content of this article. I hope it will help you learn python programming.