07 - Strings III - string methods.ipynb

Kernel: Python 3 (system-wide)

Strings III - manipulating and interrogating strings with string methods

There are a many ways in Python to manipulate and interrogate strings; these are called string methods. There are far too many to cover in this course. We will look at a couple now, which we will use in the course, and you can google others as they become necessary.

A method is applied to a string or string variable by using dot notation after the string or string variable.

Getting the index of a character or substring

In the last Notebook we used indicies to access characters and substrings within a string. We can also do the opposite and find the index of a character or substring within a string. We use the method find() to get the index of the first occurrence of a substring.

Run the code below to see how this works.

sentence = 'Hello, world!'

# Find the index of the character '!' in the variable sentence and assign it to the variable called idx.
idx = sentence.find('!')

print( f'"!" is at index {idx}' )

# Find the index of the substring 'world' in the variable sentence.
idx = sentence.find('world')

print( f'"world" begins at index {idx}' )

"!" is at index 12
"world" begins at index 7

If the character or substring we're searching for doesn't exist within the string then find() returns -1 as shown in the following code:

# Find the index of the substring 'today' in the variable sentence.
idx = sentence.find('today')

print( idx )

-1

Converting a string to lowercase

Here is an example in which we convert all the letters in a string to lowercase.

Run the following code to see how to convert all letters in a string to lowercase.

name = 'HARRY POTTER'

# The lower() method returns a string converted to lowercase.
lowercase_name = name.lower()

print(lowercase_name)

harry potter

A full list of string functions and methods is available in the Python 3 documentation.

Exercise Notebook

Strings III - string methods

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