Python Learning (8) string

Directory

• Python string
• Python accesses a value in a string
• Python string Update
• Python Escape character
• Python string operator
• Python string Formatting
• Python Triple Quote
• Unicode string
• Built-in functions for Python strings

Pythonstring

The string is the most commonly used data type in Python. We can use quotation marks (' or ') to create a string.

Creating a string is simple, as long as you assign a value to the variable. For example:

var1 = ' Hello world! ' VAR2 = "Python Runoob"

Python accesses a value in a string

Python does not support single character types, and one character is also used as a string in Python.

Python accesses substrings, you can use square brackets to intercept strings, as in the following example:

Results:

var1[0]:  Hvar2[1:5]: ytho       

Python string update

You can modify the existing string and assign it to another variable, as in the following example:

Result of the above instance execution

Update String  :-  Hellorunoob!

Python escape character

Python uses a backslash (\) to escape characters when special characters are needed in characters. As the following table:

Escape Character	Description
\ (at end of line)	Line continuation character
\\	Backslash symbol
\‘	Single quotation marks
\"	Double quotes
\a	Bell
\b	BACKSPACE (Backspace)
\e	Escape
\000	Empty
\ n	Line break
\v	Portrait tab
\ t	Horizontal tab
\ r	Enter
\f	Page change
\oyy	Octal number, the character represented by YY, for example: \o12 for newline
\xyy	Hexadecimal number, the character represented by YY, for example: \x0a for line break
\other	Other characters are output in normal format

Python string operator

The following table instance variable a value is the string "Hello" and the B variable value is "Python":

operator	description	instance
+	string Connection	A + B output Result: Hellopython
*	repeating output string	a*2 output: Hellohello
[]	Get the character	a[1] Output from the string by index   e
[:]	truncate part of the string /td>	a[1:4] Output ell
in	member operator-returns TRUE if the string contains the given character	Strong>h in a   output 1
not in	member operator-returns TRUE if the string does not contain the given character	m not in a   output 1
r/r	Raw String-Original string: All strings are used directly in the literal sense, No Escapes characters that are special or cannot be printed. The original string has almost exactly the same syntax as a normal string, except that the first quotation mark of the string is preceded by With the letter "R" (which can be case).	print R ' \ n '   output \ n and   print R ' \ n ' output \ n
%	format string	see next chapter

Instance:

Results:

A+ b  output:  hellopython< Span class= "PLN" >a * 2  Output:  hellohelloa[1< Span class= "pun" >]  output:  Ea[ 1:4]  output:  Ellh  in variable  a m  not variable  a  \n\n     

Python string formatting

Python supports the output of formatted strings. Although this may use a very complex expression, the most basic usage is to insert a value into a string that has the string format of%s.

In Python, string formatting uses the same syntax as the sprintf function in C.

The following example:

The result of the above example output:

My is Zara and is + kg!      

Python string formatting symbols:

symbols	Description
%c	Formatting characters and their ASCII code
%s	formatting strings
%d	formatting integers
%u	Formatting an unsigned integer
%o	Formatting an unsigned octal number
%x	formatting unsigned hexadecimal numbers
%x	Format unsigned hexadecimal number (uppercase)
%f	Format floating-point numbers to specify the precision after a decimal point
%e	Format floating-point numbers with scientific notation
%E	function with%e, format floating-point numbers with scientific notation
%g	Shorthand for%f and%e
%G	Shorthand for%f and%E
%p	Format the address of a variable with hexadecimal number

Formatting operator Auxiliary directives:

symbols	function
*	Define width or decimal precision
-	Used for left justification
+	Show plus sign (+) in front of positive number
<sp>	Show spaces in front of positive numbers
#	Displays 0 (' 0 ') before the octal number, preceded by ' 0x ' or ' 0X ' in hexadecimal (depending on ' x ' or ' x ')
0	The displayed number is preceded by ' 0 ' instead of the default space
%	' percent ' output a single '% '
(VAR)	mapping variables (dictionary parameters)
M.N.	M is the minimum total width displayed, and n is the number of digits after the decimal point (if available)

Python three-quote (triple quotes)

Three quotation marks in Python can be used to copy complex strings:

Python three quotes allow a string to span multiple lines, and the string can contain line breaks, tabs, and other special characters.

The syntax for a triple quotation mark is a pair of consecutive single or double quotes (usually paired).

>>>=' Hi there '>>># repr ()' Hi\nthere '>>>Print # str ()         

Three quotes allow programmers to escape from the mire of quotes and special strings, keeping a small piece of string in the form of what is known as WYSIWYG.

A typical use case is that when you need a piece of HTML or SQL, a special string escape is cumbersome when you use a string combination.

Unicode string

Defining a Unicode string in Python is as simple as defining a normal string:

>>> u' Hello world! ' u' Hello world! '   

The lowercase "u" before the quotation mark indicates that a Unicode string is created here. If you want to add a special character, you can use Python's Unicode-escape encoding. As shown in the following example:

>>> u' Hello\u0020world! ' u' Hello world! '   

The replaced \u0020 ID indicates that a Unicode character (a blank space) with encoded values of 0x0020 is inserted at the given location.

Python string built-in functions

String methods are slowly added from python1.6 to 2.0-they are also added to Jython.

These methods implement most of the methods of the string module, as shown in the following table, which lists the currently supported methods for string literals, all of which contain support for Unicode, and some are even specifically for Unicode.

Method	Description
String.capitalize ()	Capitalize the first character of a string
String.center (width)	Returns the center of the original string and fills the new string with a space of length width
String.count (str, beg=0, End=len (String))	Returns the number of occurrences of STR in a string, if beg or end specifies that the number of STR occurrences in the specified range is returned
String.decode (encoding= ' UTF-8 ', errors= ' strict ')	Decodes a string in the encoded format specified by encoding, if an error defaults to a ValueError exception unless errors specifies ' ignore ' or ' replace '
String.encode (encoding= ' UTF-8 ', errors= ' strict ')	Encodes a string in the encoding format specified by encoding, if an error defaults to a ValueError exception unless errors specifies ' ignore ' or ' replace '
String.endswith (obj, beg=0, End=len (String))	Checks whether the string ends with obj, or returns False if beg or end specifies whether to end with obj in the specified range, or True if it is.
String.expandtabs (tabsize=8)	Turns the tab symbol in string strings to a space, and the default number of spaces for the tab symbol is 8.
String.find (str, beg=0, End=len (String))	Detects if STR is contained in a string, and if beg and end specify a range, the check is contained within the specified range, and returns 1 if the index value is returned.
String.index (str, beg=0, End=len (String))	Just like the Find () method, only if STR does not report an exception in string.
String.isalnum ()	If the string has at least one character and all characters are letters or numbers, return Return True, otherwise False
String.isalpha ()	Returns True if the string has at least one character and all characters are letters. otherwise returns False
String.isdecimal ()	Returns True if the string contains only a decimal number, otherwise False.
String.isdigit ()	Returns True if the string contains only a number, otherwise False.
String.islower ()	Returns True if the string contains at least one case-sensitive character, and all of these (case-sensitive) characters are lowercase, otherwise False
String.isnumeric ()	Returns True if the string contains only numeric characters, otherwise False
String.isspace ()	Returns True if the string contains only spaces, otherwise False is returned.
String.istitle ()	Returns True if string is heading (see Title ()), otherwise False
String.isupper ()	Returns True if the string contains at least one case-sensitive character, and all of these (case-sensitive) characters are uppercase, otherwise False
String.Join (seq)	Merges all the elements in the SEQ (the string representation) into a new string, using string as a delimiter
String.ljust (width)	Returns the left alignment of an original string and fills the new string with the width of length with a space
String.Lower ()	Converts all uppercase characters in a string to lowercase.
String.lstrip ()	Truncate the left space of a string
String.maketrans (Intab, Outtab])	The Maketrans () method is used to create a conversion table of character mappings, for the simplest invocation of two parameters, the first argument is a string that represents the character that needs to be converted, and the second argument is the target of the string representation of the transformation.
Max (str)	Returns the largest letter in the string str .
Min (str)	Returns the smallest letter in the string str .
String.partition (str)	A bit like the combination of find () and split (), from the first position where Str appears, divide the string into a 3-element tuple (STRING_PRE_STR,STR,STRING_POST_STR), if string STR is not included in the STRING_PRE_STR = = string.
String.Replace (str1, str2, Num=string.count (STR1))	Replace the str1 in string with the str2, if NUM is specified, the replacement is no more than num times.
String.rfind (str, Beg=0,end=len (String))	Similar to the Find () function, it is just looking from the right.
String.rindex (str, Beg=0,end=len (String))	Similar to index (), but starting from the right.
String.rjust (width)	Returns the right alignment of the original string and fills the new string with the width of the length with a space
String.rpartition (str)	Similar to the partition () function, it is just looking from the right.
String.rstrip ()	Removes a space at the end of a string string.
String.Split (str= "", Num=string.count (str))	Slice string with a delimiter of STR, if NUM has a specified value, only the NUM substring is delimited
String.splitlines (Num=string.count (' \ n '))	Returns a list that contains rows as elements, separated by rows, and if num specifies that only num rows are sliced.
String.startswith (obj, Beg=0,end=len (string))	Checks whether the string starts with obj, returns True, or False. If beg and end specify a value, the check is within the specified range.
String.strip ([obj])	Execute Lstrip () and Rstrip () on string
String.swapcase ()	Flip the case in a string
String.title ()	A string that returns "header", meaning that all words start with uppercase and the remaining letters are lowercase (see istitle ())
String.translate (str, del= "")	Converts a string of characters according to the table given by STR, which contains 256 characters, The characters to filter out are placed in the Del parameter
String.upper ()	Convert lowercase letters in string to uppercase
String.zfill (width)	Returns a string of length width, the original string is right-aligned, and the front padding is 0
String.isdecimal ()	The Isdecimal () method checks whether a string contains only decimal characters. This method exists only in Unicode objects.

Python Learning (8) string