Strings and String Operations in Python

 Strings and String Operations in Python

What are the strings ?

In Python, strings are sequences of characters that can be used to store and manipulate text. They are commonly used to represent words, sentences and other pieces of text in a program. Python strings is a collection of Unicode characters.

String properties

Python strings can be enclosed in single, double or triple quotes.

 print('Hello World')
 print("Hello World")
 print('''Hello World''')
 print("""Hello World""")
 
 //Output
 Hello World
 Hello World
 Hello World
 Hello World

Python strings are immutable

An object whose internal state can be changed is mutable. On the other hand, immutable doesn't allow any change in the object once it has been created. So the strings are immutable in Python they doesn't allow any change in the object.

Example :

x = "Hello World"
x = "Hello"
x[0] = M
print(x)

//Output
TypeError: 'str' object does not support item assignment

String concatenation

Strings can be concatenated using + operator, by using this operator we can able to concate two or more strings, words, and characters.

Example :

first_name = "Elon"
last_name = "-Musk"
full_name = first_name + last_name
print(full_name)
 
//Output
Elon-Musk

String slicing

In Python, string slicing is a way to extract a portion of a string by specifying the start and end index of the characters you want to extract.

Syntax :

string[start: end: step]

Where "string" is the name of the string variable, "start" is the index of the first character to include in the slice, and "end" is the index of the first character to exclude from the slice.

In Python, strings can be indexed using either positive or negative numbers.

A positive index refers to the position of an element in a string, starting from 0 for the first character.

From the first table the string "ASTRING" has a 'A'  at index 0, 'S' at index 1, and so on.

A negative index refers to the position of an element in a string, starting from -1 for the last character.

From the second table the string "ASTRING" has a 'G' at index -1, 'N' at index -2, and so on.

String slicing is a way to extract a portion of a string by specifying a start and end index.

Here, are some examples of string slicing in Python

1. Extracting a single character :

string = "hello"
char = string[1]
print(char)  

//Output
"e"

2. Extracting a substring :

string = "hello world"
substring = string[7:12]
print(substring)    
 
//Output
"world"

3. Extracting a substring from the end of the string :

string = "hello world"
substring = string[-6:]
print(substring)  

//Output
"world"

4. Extracting a substring from the start of the string :

string = "hello world"
substring = string[:5]
print(substring) 

//Output
"hello

5. Extracting every nth character :

string = "hello world"
substring = string[::2]
print(substring)  

//Output
"hlowrd"

6. Extracting a substring in reverse order :

string = "hello world"
 substring = string[::-1]
 print(substring)  

 //Output
 "dlrow olleh"

7. Extracting a substring using both positive and negative indexing :

string = "hello world"
substring = string[-6:5]
print(substring)  

//Output
"wor"

Strings Methods

In Python, strings have several built-in methods that can be used to perform various operations on them.

Methods	Description
capitalize()	Converts the first character to upper case
casefold()	Converts string into lower case
center()	Returns a centered string
count()	Returns the number of times a specified value occurs in a string
encode()	Returns an encoded version of the string
endswith()	Returns true if the string ends with the specified value
expandtabs()	Sets the tab size of the string
find()	Searches the string for a specified value and returns the position of where it was found
format()	Formats specified values in a string
format_map()	Formats specified values in a string
index()	Searches the string for a specified value and returns the position of where it was found
isalnum()	Returns True if all characters in the string are alphanumeric
isalpha()	Returns True if all characters in the string are in the alphabet
isascii()	Returns True if all characters in the string are ascii characters
isdecimal()	Returns True if all characters in the string are decimals
isdigit()	Returns True if all characters in the string are digits
isidentifier()	Returns True if the string is an identifier
islower()	Returns True if all characters in the string are lower case
isnumeric()	Returns True if all characters in the string are numeric
isprintable()	Returns True if all characters in the string are printable
isspace()	Returns True if all characters in the string are whitespaces
istitle()	Returns True if the string follows the rules of a title
isupper()	Returns True if all characters in the string are upper case
join()	Converts the elements of an iterable into a string
ljust()	Returns a left justified version of the string
lower()	Converts a string into lower case
lstrip()	Returns a left trim version of the string
maketrans()	Returns a translation table to be used in translations
partition()	Returns a tuple where the string is parted into three parts
replace()	Returns a string where a specified value is replaced with a specified value
rfind()	Searches the string for a specified value and returns the last position of where it was found
rindex()	Searches the string for a specified value and returns the last position of where it was found
rjust()	Returns a right justified version of the string
rpartition()	Returns a tuple where the string is parted into three parts
rsplit()	Splits the string at the specified separator, and returns a list
rstrip()	Returns a right trim version of the string
split()	Splits the string at the specified separator, and returns a list
splitlines()	Splits the string at line breaks and returns a list
startswith()	Returns true if the string starts with the specified value
strip()	Returns a trimmed version of the string
swapcase()	Swaps cases, lower case becomes upper case and vice versa
title()	Converts the first character of each word to upper case
translate()	Returns a translated string
upper()	Converts a string into upper case
zfill()	Fills the string with a specified number of 0 values at the beginning

Escape sequences

In Python, an escape sequence is a combination of characters that represents a special character. Escape sequences are used to represent characters that are not easily entered into a string, such as newline, tab, or quotes.

Here, are some examples of commonly used escape sequences

1) \n : represents a newline character. It is used to insert a new line in a string.

string = "Hello\nWorld"
print(string)
 
//Output: 
Hello
World

2) \t : represents a tab character. It is used to insert a tab space in a string.

string = "Hello\tWorld"
print(string)

//Output: 
Hello    World

3) \" : represents a double quote character. It is used to include a double quote within a string that is enclosed in double quotes.

string = "He said, \"Hello World\""
 print(string)

 //Output: 
 He said, "Hello World"

4) \\ : represents a backslash. It is used to include a backslash within a string.

string = "Hello\\World"
print(string)

//Output: 
Hello\World

5) /r : represents a Carriage return. It is used to move the cursor to the beginning of the current line.

string = "Hello\rWorld"
print(string)

//Output: 
WorldolleH

These are just a few examples of escape sequences in Python. There are other escape sequences available as well, such as '\a','\b','\f','\v', etc. Each escape sequence has a specific use case, and it's good to familiarize yourself with them to be able to use the appropriate one for a specific task.

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