String

Strings in Python

In the previous blog Data Types, we explored Strings in Python, and in this blog let’s dig a bit deeper into strings and what we can do with them.
A string in Python is an array (or list) of characters, and in Python, a single character is still considered as a string with only one letter. This is an important distinction as in other programming languages, there is the “char” datatype which stores only one character.
Consider a string with the text “Verification Master”, and look at the image below to see their respective index numbers.

Since a string in python is an array we access it by specifying the index number.

string_variable = "Verification Master"

print(string_variable[5]) # This should print "i"

If we want to access a set of characters, we simply add the index of the character till which we require.

string_variable = "Verification Master"

print(string_variable[3:14])

The output would be

NOTE: If you are still confused why “a” wasn’t printed as well, remember that in a range if the endpoint is “n” then Python stops at “n-1”. Here n is 14, and so Python will stop at index 13.

We can see the length of a string using the len() function. The len() function prints the number of items in a string.

string_variable = "Verification Master"

print(len(string_variable)) # This would print 19

We can also use Python to check if a certain text (sub-string) is contained within a larger text.

sample_string = "Python; simple to learn programming language"

print("simple" in sample_string) # This should print True

Strings functions

Python offers a range of built-in functions that we can use with strings, and so we won’t be able to explore every one of these, but we will explore a select few to understand how to accurately use such a function.
capitalize(): Allows us to capitalize the first letter of the text.

sample_string = "python is a simple to learn programming language"

sample_string = sample_string.capitalize()
print(sample_string)

Here we are capitalizing the first letter of the string and storing the capitalized result in the same variable.

• islower()/isupper(): Checks if the string is in lowercase/uppercase respectively.

test_string = "python"

print(test_string.islower())
print(test_string.isupper())

This would print True first and then False, as test_string contains a value that is in lowercase.

• count(): Counts the number of occurrences of a sub-string within a string. The sub-string can even contain only one string.

sample_string = "python is a simple to learn programming language"

count = sample_string.count("py")
print(count) # Prints 1

• • count(value, start, end)
    • value – This is the sub-string we want to find in the original string. (mandatory)
    • start – This parameter allows us to start our search from a specific index. (optional)
    • end – This parameter allows us to end our search at a specific index. (optional)

count = sample_string.count("py", 3, 15)
print(count) # Prints 0 since we are only starting the search after index 3

• lower()/upper(): Converts the string to lowercase/uppercase characters respectively.

test_string = "PyThoN"

print(test_string.upper())
print(test_string.lower())

• index(): Provides us the index of the sub-string

Consider the following table which covers a few more of the available built-in string functions.

What have we learned?

.How to use a select letter of a string?
.How to see the length of a string?
.How to check if a substring exists in a string?
.How to check the index value of a substring?
.How does the find() differ from the index()?