Strings in python

V.M.Prabhakaran,
Department Of Cse,
KIT- Coimbatore
Problem Solving and Python Programming 1

Strings: string slices, immutability,
string functions and methods, string
module

Strings
• String is a sequence of characters.
• String may contain alphabets, numbers and
special characters.
• Usually strings are enclosed within a single
quotes and double quotes.
• Strings is immutable in nature.
• Example:
a=„hello world‟
b=“Python”

Inbuilt String functions
• Python mainly contains 3 inbuilt string functions.
• They are
– len()
– max()
– min()
• len()- Find out the length of characters in string
• min()- Smallest value in a string based on ASCII values
• max()- Largest value in a string based on ASCII values

What is ASCII values

Example for Inbuilt string functions
name=input("Enter Your name:")
print("Welcome",name)
print("Length of your name:",len(name))
print("Maximum value of chararacter in your name",
max(name))
print("Minimum value of character in your name",min(name))

OUTPUT
Enter Your name:PRABHAKARAN
Welcome PRABHAKARAN
Length of your name: 11
Maximum value of chararacter in your name R
Minimum value of character in your name A

Strings Concatenation
• The + operator used for string concatenation.
Example:
a=“Hai”
b=“how are you”
c=a+b
print(c)

Operators on String
• The Concatenate strings with the “*” operator
can create multiple concatenated copies.
• Example:
>>> print("Python"*10)
PythonPythonPythonPythonPythonPython
PythonPythonPythonPython

String Slicing
• Slicing operation is used to return/select/slice
the particular substring based on user
requirements.
• A segment of string is called slice.
• Syntax: string_variablename [ start:end]

String Slice example
s=“Hello”
H e l l o
0 1 2 3 4
-5 -4 -3 -2 -1

Strings are immutable
• Strings are immutable character sets.
• Once a string is generated, you cannot change
any character within the string.

String Comparision
• We can compare two strings using comparision
operators such as ==, !=, <,<=,>, >=
• Python compares strings based on their
corresponding ASCII values.

Example of string comparision
str1="green"
str2="black"
print("Is both Equal:", str1==str2)
print("Is str1> str2:", str1>str2)
print("Is str1< str2:", str1<str2)
OUTPUT:
Is both Equal: False
Is str1> str2: True
Is str1< str2: False

String formatting operator
• String formatting operator % is unique to
strings.
• Example:
print("My name is %s and i secured %d
marks in python” % ("Arbaz",92))
• Output:
My name is Arbaz and i secured 92 marks in
python

String functions and methods
len() min() max() isalnum() isalpha()
isdigit() islower() isuppe() isspace() isidentifier()
endswith() startswith() find() count() capitalize()
title() lower() upper() swapcase() replace()
center() ljust() rjust() center() isstrip()
rstrip() strip()

i) Converting string functions
captitalize() Only First character capitalized
lower() All character converted to lowercase
upper() All character converted to uppercase
title() First character capitalized in each word
swapcase() Lower case letters are converted to
Uppercase and Uppercase letters are
converted to Lowercase
replace(old,new) Replaces old string with nre string

Program:
str=input("Enter any string:")
print("String Capitalized:", str.capitalize())
print("String lower case:", str.lower())
print("String upper case:", str.upper())
print("String title case:", str.title())
print("String swap case:", str.swapcase())
print("String replace case:",str.replace("python","python programming"))
Output:
Enter any string: Welcome to python
String Capitalized: Welcome to python
String lower case: welcome to python
String upper case: WELCOME TO PYTHON
String title case: Welcome To Python
String swap case: wELCOME TO PYTHON
String replace case: Welcome to python programming

ii)Formatting String functions
center(width) Returns a string centered in a field of given width
ljust(width) Returns a string left justified in a field of given width
rjust(width) Returns a string right justified in a field of given width
format(items) Formats a string

Program:
a=input("Enter any string:")
print("Center alignment:", a.center(20))
print("Left alignment:", a.ljust(20))
print("Right alignment:", a.rjust(20))
Output:

iii) Removing whitespace
characters
lstrip()
Returns a string with
leading whitespace
characters removed
rstrip()
trailing whitespace
characters removed
strip()
leading and trailing
whitespace characters
removed

Program
print("Left space trim:",a.lstrip())
print("Right space trim:",a.rstrip())
print("Left and right trim:",a.strip())
Output:

iv) Testing String/Character
isalnum()
Returns true if all characters in string are alphanumeric and there is
atleast one character
isalpha()
Returns true if all characters in string are alphabetic
isdigit()
Returns true if string contains only number character
islower()
Returns true if all characters in string are lowercase letters
isupper()
Returns true if all characters in string are uppercase letters
isspace() Returns true if string contains only whitespace characters.

Program
print("Alphanumeric:",a.isalnum())
print("Alphabetic:",a.isalpha())
print("Digits:",a.isdigit())
print("Lowecase:",a.islower())
print("Upper:",a.isupper())
Output:

v) Searching for substring
Endswith() Returns true if the strings ends with the substring
Startswith()
Returns true if the strings starts with the substring
Find()
Returns the lowest index or -1 if substring not found
Count() Returns the number of occurrences of substring

Program
print("Is string ends with thon:", a.endswith("thon"))
print("Is string starts with good:", a.startswith("good"))
print("Find:", a.find("ython"))
print("Count:", a.count(“o"))
Output:
Enter any string : welcome to python
Is string ends with thon: True
Is string starts with good: False
Find: 12
Count: 3

String Modules
• String module contains a number of functions to
process standard Python strings
• Mostly used string modules:
string.upper()
string.upper()
string.split()
string.join()
string.replace()
string.find()
string.count()

Example
import string
text="Monty Python Flying Circus"
print("Upper:", string.upper(text))
print("Lower:", string.lower(text))
print("Split:", string.split(text))
print("Join:", string.join(string.split(test),"+"))
print("Replace:", string.replace(text,"Python", "Java"))
print("Find:", string.find(text,"Python"))
print("Count", string.count(text,"n"))

Output
Upper: “MONTY PYTHON FLYING CIRCUS”
Lower: “monty python flying circus”
Split: [„Monty‟, „Python‟, „Flying‟, „Circus‟]
Join : Monty+Python+Flying+Circus
Replace: Monty Java Flying Circus
Find: 7
Count: 3

Strings in python

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