Python Strings

What is Data Type?

It is an attribute that tells what kind of data that value or a variable can have it.

#Example:
rollnumber  = 12345 # rollnumber  is integer
name = "Anand" # name is string
marks = 80.5  # marks is float

Standard Data Types

Numbers
Strings
List
Tuple
Dictionary

Python Strings

A string is a sequence of characters.

It is represented by either single quotation marks, or double quotation marks.

Even triple quotes can be used in Python but generally used to represent multiline strings and docstrings.

Note: Python doesn’t have any separate data type for characters so they are represented as a single character string

How to create a python string?

#Sample Code
singlequote = 'Python String'
print(singlequote)

doublequote = "Python Tutorials"
print(doublequote)

# triple quotes string can extend multiple lines
triplequote = """Welcome to Vinoth Rathinam
                    Tutorials"""
print(triplequote)

Output:
Python String
Python Tutorials
Welcome to Vinoth Rathinam
                    Tutorials

Accessing Values in Strings (Slicing)

We can access individual characters using indexing and a range of characters using slicing.

Index starts from 0.

Left to right direction

#Sample Code
myString = "Python for Machine Learning"

#print first Character
print(myString[0])

#slicing 11th to 18th characters
print(myString[11:18])

# Using the defalut values - Use it as per the requirement
print(myString[:])
print(myString[11:]) 
print(myString[:11])

Output:
P
Machine
Python for Machine Learning
Machine Learning
Python for

Negative Indexing

Python allows negative indexing for its sequences.

Index starts from -1

Right to left direction

The index of -1 refers to the last item, -2 to the second last item and so on

# Sample code to slice the strings
myString2 = "Python for Automation"

#print last character using negative indexing
print(myString2[-1])

print(myString2[-2])

print(myString2[-5])

#slicing 7th to 2nd last character
print(myString2[7:-2])

Output:
n
o
a
for Automati

Index out of the range

If we try to access index out of the range or use decimal number, we will get "IndexError"

The index must be an integer. We can't use float or other types, this will result into TypeError.

Python allows negative indexing for its sequences

# Sample code for IndexError
myString3 = "Python"
print(myString3[6])

Output:
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-25-4f411a63679a> in <module>()
      1 # Sample code for IndexError
      2 myString3 = "Python"
----> 3 print(myString3[6])

IndexError: string index out of range

# Sample code for TypeError
print(myString2[1.5])

Output:
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-26-3f161d7da838> in <module>()
      1 # Sample code for TypeError
----> 2 print(myString2[1.5])

TypeError: string indices must be integers

How to change or update a string ?

Strings are immutable. This means that elements of a string cannot be changed once it has been assigned.

We can simply reassign different strings to the same name.

# Creating a string and checking the memory address
str1 = "Python "
print(str1)
print("Memory location before update",id(str1))

# Trying to modify the string
str1 += "Tutorials"  # str1 = str1 + "Tutorials"
print(str1)
print("Memory location after update",id(str1))

Output:
Python 
Memory location before update 1825268075800
Python Tutorials
Memory location after update 1825268818328

# Updating the String Value
myStr = "Happy Learning"
print(myStr)
myStr[4] = 's'

Output:
Happy Learning
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-29-85c0b5e71d2c> in <module>()
      2 myStr = "Happy Learning"
      3 print(myStr)
----> 4 myStr[4] = 's'

TypeError: 'str' object does not support item assignment

How to Delete a String?

We cannot delete or remove characters from a string.

We can delete the string entirely using the keyword "del"

# Code to delete complete string
del myStr
print(myStr)

Output:
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-31-ede3757523fc> in <module>()
----> 1 print(myStr)

NameError: name 'myStr' is not defined