String In Python

aimtocode

String Definition

A string is a sequence of characters. You can access the characters one at a time with the bracket operator:


Python String Indexing

The index() method finds the first occurrence of the specified value, and this method raises an exception if the value is not found.

The index() method is almost the same as the find() method, the only difference is that the find() method returns -1 if the value is not found.

Syntax

 string.index(value, start, end)

Parameters:


Parameters Description
str This specifies the string to be searched.
start Specify the start of the search. By default is 0
end This is the ending index, by default its equal to the length of the string.


Example:

 var = "welcome Coding lover."
 obj = var.index("lover")
 print(obj)

Output:

 15


Accessing Values in Strings

 subject = 'python'
 tutor = "aimtocode"
 print("Subject: ",subject)
 print("Tutor: ", tutor)

Output:

 Subject:  python
 Tutor:  aimtocode

As you can see, string 'python' is assigned with 'subject' variable followed by equal sign, and string "aimtocode" is assigned with tutor variable, python can accept both single quotes(' ') and double quotes(" ") as well to assigne the numbers of characters as a string.

Python does not support a character type; these are treated as strings of length one, however it is also considered as a substring.

A segment of a string is called a slice. Selecting a slice is similar to selecting a character:


Assigning Multiline Strings

 a = """Python can have multiple line
 as string by using triple double quotes,
 """
 print(a)

Output:

 Python can have multiple line
 as string by using triple double quotes,


Traversal with a for Loop

A lot of computations involve processing a string one character at a time. Often they start at the beginning, select each character in turn, do something to it, and continue until the end. This pattern of processing is called a traversal. One way to write a traversal is with a while loop:

Example:

 subject ="Aimtocode"
 index = 0
 while index < len(subject):
     letter = subject [index]
     print(letter)
     index = index + 1	 


Output:

 A
 i
 m
 t
 o
 c
 o
 d
 e

This loop traverses the string and displays each letter on a line by itself.

The loop condition is index < len(subject), so when index is equal to the length of the string, the condition is false, and the body of the loop doesn’t run.

The last character accessed is the one with the index len(subjec)-1, which is the last character in the string.

Another way to write a traversal is with a for loop:

 subject="Aimtocode"
	for letter in subject:
	print(letter)

subject ➝ A i m t o c o d e
Index 0 1 2 3 4 5 6 7 8


String Operators

The in Operator

The word in is a boolean operator that takes two strings and returns True if the first appears as a substring in the second:

 't' in 'python'
 True
 'jan' in 'python'
 False

Operator Description
+ Concatenate strings given either side of the operator.
* It is known as repetition operator. It concatenates the multiple copies of the same string.
[] It is known as slice operator. It is used to access the sub-strings of a particular string.
[:] Range slice operator is used to access the characters from the specified range.
in Membership operator is used to returns if a particular sub-string is present in the specified string.
not in It is also a membership operator and does the exact reverse of in. It returns true if a particular substring is not present in the specified string.
r/R It is used to specify the raw string. Raw strings are used in the cases where we need to print the actual meaning of escape characters such as "C://python". To define any string as a raw string, the character r or R is followed by the string.
% Ued to perform string formatting. It is similar to format specifiers used in C programming like %d or %f to map their values in python.

String Methods

A method is similar to a function it takes arguments and returns a value but the syntax is different.

For example, the method upper takes a string and returns a new string with all uppercase letters. Instead of the function syntax upper(word), it uses the method syntax word.upper().


String Formatting Operator


Format Symbol Conversion
%c character
%s string conversion via str() prior to formatting
%i signed decimal integer
%d signed decimal integer
%u unsigned decimal integer
%o octal integer
%x hexadecimal integer (lowercase letters)
%X hexadecimal integer (UPPERcase letters)
%e exponential notation (with lowercase 'e')
%E exponential notation (with UPPERcase 'E')
%f floating point real number
%g the shorter of %f and %e
%G the shorter of %f and %E


List of String Methods

SN Methods Description
1 capitalize() Capitalizes first letter of 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 errors is given with 'ignore' or 'replace'.
6 endswith(suffix,
beg=0,
end=len(string))
Determines if string or a substring of string (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(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 at least 1 character and all characters are alphabetic and false otherwise.
12 isdigit() Returns true if string contains only digits and false otherwise.
13 islower() Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise.
14 isnumeric() Returns true if a unicode string contains only numeric characters and false otherwise.
15 isspace() Returns true if string contains only whitespace characters and false otherwise.
16 istitle() Returns true if string is properly "titlecased" and false otherwise.
17 isupper() Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise.
18 join(seq) Merges (concatenates) the string representations of elements in sequence seq into a string, with separator string.
19 len(string) Returns the length of the string
20 ljust(width[, fillchar]) Returns a space-padded string with the original string left-justified to a total of width columns.
21 lower() Converts all uppercase letters in string to lowercase.
22 lstrip() Removes all leading whitespace in string.
23 maketrans() Returns a translation table to be used in translate function.
24 max(str) Returns the max alphabetical character from
25 min(str) Returns the min alphabetical character from the string str.
26 replace(old, new [, max]) Replaces all occurrences of old in string with new or at most max occurrences if max given.
27 rfind(str, beg=0,
end=len(string))
Same as find(), but search backwards in string.
28 rindex(str,beg=0,
end=len(string))
Same as index(), but search backwards in string.
29 rjust(width,[, fillchar]) Returns a space-padded string with the original string right-justified to a total of width columns.
30 rstrip() Removes all trailing whitespace of string.
31 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.
32 splitlines( num=
string.count('\n'))
Splits string at all (or num) NEWLINEs and returns a list of each line with NEWLINEs removed.
33 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 otherwise.
34 strip([chars]) Performs both lstrip() and rstrip() on string
35 swapcase() Inverts case for all letters in string.
36 title() Returns "titlecased" version of string, that is, all words begin with uppercase and the rest are lowercase.
37 translate(table,
deletechars="")
Translates string according to translation table str(256 chars), removing those in the del string.
38 upper() Converts lowercase letters in string to uppercase.
39 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).
40 isdecimal() Returns true if a unicode string contains only decimal characters and false otherwise.
aimtocode