String datatype in Python || Python for beginners

String

• String are the sequence of zero or more characters represented with in quotation marks. An empty string contains no character and has a length 0
• The indices of a string’s characters are numbered from 0 from the left end and numbered from -1 from the right end.

Character	W	E	L	C	O	M	E
Index from left end	0	1	2	3	4	5	6
Index from right end	-7	-6	-5	-4	-3	-2	-1

Subscript Operator

1. [ ] is a subscript operator that is used to access the characters at a time.
2. Index within [ ] indicated the position of the particular character in the string and it must be an integer expression.

Syntax:

<stringname>[<index>]

Program 

s=“HELLO”

s[0]

print(s[3])

Output

H

L

Len funtion

len is a built-in function that return the number of character in a string

Program

s=“HELLO PYTHON!”

print(“Length is”,len(s))

Output 

Length is 13

In operators

• “in” is a Boolean operator that takes two strings as its operands and returns True if tha first string appears as a substring in the second string.

Program

print(“PY” in “HELLO PYTHON!”)

“NO” in “HELLO PYTHON!”

Output 

True

False

String slices

• A part of a sting is called slice. The operator [m:n] returns the part of the string from 𝑚^𝑡ℎ index to 𝑛^𝑡ℎ index, including the character at 𝑚^𝑡ℎ index but excluding the character at 𝑛^𝑡ℎ index.
• If the first index is omitted, the slice starts at the beginning of the string. If the second index is omitted, the slice starts at the beginning of the string. 
• If the first index is grater than or equal to the second, the slice is an empty string. If both indices are omitted, the slice is given string itself.

Program 

str=‘Hello World’

Code	Output
print(str)	Hello World
print(str[0])	H
print(str[-1])	d
print(str[1:5])	ello
print(str[2:])	llo World
print(str[3:3])
print(str[:])	Hello World
print(str[-3:])	rld

Ability 

A string is an immutable data structure. This means that its characters can be accessed but the string cannot be modified

Program:

s=‘hello python’

s[0]=‘H’

Output

TypeError:’str’ object does not support item assignment

s=‘hello python’

s1=‘H’+s[1:len(s)]

print(s)

print(s1)

Output

hello python

Hello python

String Methods

Built-in String Methods

Python includes the following built-in methods to manipulate strings

 

S.NO.	Method	Description
1	capitalize()	Capitalizes the first letter of the string.
2	center(width, fillchar)	Returns a space-padded string with the original string centered to a total of width columns.
3	count(str, beg=0, end=len(string))	Counts how many times str occurs in string or in a substring of string if starting index beg and ending index end are given.
4	decode(encoding='UTF-8', errors='strict')	Decodes the string using the codec registered for encoding. Encoding defaults to the default string encoding.
5	encode(encoding='UTF-8', errors='strict')	Returns encoded string version of string; on error, default is to raise a ValueError unless error is given with 'ignore' or 'replace'.
6	endswith(suffix, beg-=0 , end=len(string))	Determines if string or a substring (if starting index beg and ending index end are given) ends with suffix; returns true if so and false otherwise.
7	expandtabs(tabsize=8)	Expands tabs in string to multiple spaces; defaults to 8 spaces per tab if tabsize not provided.
8	find(str, beg=0, end=len(string))	Determine if str occurs in string or in a substring of string if starting index beg and ending index end are given returns index if found and -1 otherwise.
9	index(str, beg=0, end=len(len(string)))	Same as find(), but raises an exception if str not found.
10	isalnum()	Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise.
11	isalpha()	Returns true if string has al least 1 character and all characters are alphabetic an false otherwise.
12	isdecimal()	Returns true if a unicode string contains only decimal characters and false otherwise
13	isdigit()	Returns true if string contains onlu digits and false otherwise.
14	islower()	Returns true if string has at lease 1 cased character and all cased characters are in lowercase and false otherwise.
15	isnumeric()	Returns ture if a unicode string contains only numeric characters and false otherwise.
16	isspace()	Returns ture if string contains only whitespace characters and false otherwise.
17	istitle()	Returns true if string is properly "titlecased" and false otherwise.
18	isupper()	Returns ture if string has at least one cased character and all cased characters are in uppercase and false otherwise.
19	join(seq)	Merges (concatenates) the string representations of elements in sequence seq into a string, with separator string.
20	len(string)	Returns the length of the string.
21	ljust(width, fillchar)	Returns a space-padded string with the original string left-justified to a total of width columns.
22	lower()	Converts all uppercase letters in string to lowercase.
23	lstrip()	Removing all leading whitespace in string.
24	maketrans()	Returns a translation table to be used in translate funtion.
25	max(str)	Returns the max alphabetical character from the string str.
26	min(str)	Returns the min alphabetical character from the string str.
27	replace(old, new, max)	Replace all occurrence of old in string with new or at most max occurrences if max given
28	rfind(str, beg=0, end=len(string))	Same as find(), but search backward in string.
29	rindex(str, beg=0, end=len(string))	Same as index(), but search backward in string.
30	rjust(width, fillchar)	Returns a space-padded string with the original string left-justified to a total of width columns.
31	rstrip()	Remove all trailing whitespace of string.
32	split(str="", num=string.count(str))	Splits string according to delimiter str(space if not provided) and returns list of substrings; split into at most num substrings if given.
33	splitlines(num=string.count(str))	Strip string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed.
34	startswith(str, beg=0, end=len(string))	Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwidsotherwise.
35	strip()	Performs both lstrip() and rstrip() on string.
36	swapcase()	Inverts case for all letters in string.
37	title()	Returns "titlecased" version of string, that is, all words begin with uppercase and the rest are lowercase/
38	translate(table, deletechars="")	Translates string according to translation table str(256 chars), removing those in del string.
39	upper()	Converts lowercase letters in string to uppercase.
40	zfill(width)	Returns original string leftpadded with zeros to a total of width characters; intended for numbers, zfill() retains any sign given (less one zero).