Python Basics 7: String part 1- Introduction

What is String?

=> String is a sequence of ordered characters(alphabets-lower case, upper case, numeric values, special symbols etc.) in a program.

It is represented with quotation marks(single(‘), double(“) or triple(‘ ‘ ‘/” ” “) at the beginning and the end. You can use either one you want.

Example:

“Hello World”
‘CSE is awesome’
“Not a valid string'(must follow one type of quotation marks)

String inside a string

To write a string inside a string, you need to use different types of quotation marks. It means that if you have a substring inside a string that is surrounded by double quotation marks, then use single quotation mark to represent the main string and vice versa.

Ex: “This is a valid ‘string’ because it maintains the order”
‘String inside a ‘string’ like this not allowed’

You can also use ‘Escape Sequence’ for that:
*If you have some special character inside your string that might confuse the interpreter, you can use ‘Escape sequence’ to clarify. Escape sequence tells the interpreter to consider the character following the backslash as a printable character.

Ex: “I love the movie \”Shang-chi\” “
‘She said that Aren\’t you going to late for work?’

More facts about string:

• A single character is also a string.
  Ex: “P”, ‘P’
• String is case sensitive.
  Ex: “A” and ‘a’ are two different strings.
• Space is also a string.
  Ex: ” ” and ‘ ‘ are strings.
• Empty string- where nothing is between the quotation marks.
  Ex: “” and ”
• “1” is not an integer, it’s a string!

String Mutability:

This is a very important concept of string. Strings are immutable. Once a string is created the characters in it can’t be changed/deleted/altered. So each time we have to modify a string, we need to make a copy of the original one and make changes to the duplicate one.

Sentence= "Loving CSE110' Sentence[0]= "M"

TypeError: ‘str’ doesn’t support item alignment.(here, we’re trying to change the string but we can’t alter any of the characters in the string)

*However, we can change the entire string.

s=’I am Baymax’

Print(s)
s=’I am Superman’
Print(s)=> Here, we have stored a completely different string in s variable.

Deletion

‘del’ = keyword to unbind reference to a string, It will delete a string from its variable.

Ex:

s='I love CSE' Print(s)
Del(s)
Print(s) >>> I love CSE
Error *We can't delete a character from a string. s='I am 007' del(s[0]) >>> ERROR

String Membership

We can use ‘in’ keyword to find if there is occurrence of any substring in a given string(whether a string is present inside another string or not).

Ex:

'bay' in 'ebay'
>>True

'bay' not in 'ebay'
>>False

*It can be used in ‘if statement’ as condition.

S1= 'I am Loki'
S2='am'
If S2 in S1: Print(found)
Else: Print(not found) >>>found

This is all for today about string. In next part, we’ll discuss more about string and it’s functions. Then we’ll try to solve some problems. Till then, keep practicing. Happy coding!