Strings

We have in Python not only top-level functions to help us manipulate strings, but also methods from the string class that are also inherited by any other string inside the code as well as string slicing and other features.

Also important to keep in mind is that none of the methods used to manipulate strings will essentially mutate the original value; instead, they will return us a new value that can be used further in the code.

Strings in Python are immutable and will always return a new value rather than mutating the original value.

String features

Before diving into string methods and its properties is worth taking a look at what is possible to do with strings other than manipulate it with functions.

String Slicing

It’s possible to pass a index inside brackets after strings, just like in lists, to return a substrings that represents the respective character of the string at that index.

name = 'Reinaldo'

print(name[0]) # 'R' will be shown on the terminal.

If you run the code above you will see at the terminal the string R, which is a substring from the string name that we set before.

This feature will follow the same rules as for lists; it means that each character inside the string is represented by an index that starts at zero, i.e., the first character has index zero and so on.

If you want, you can also pass another index after a colon to return a substring that goes from the left side index to the character that is just before the right side index within the string, e.g.

string[inclusive:exclusive]
city = 'California'

print(city[1:5]) # 'alif' will be shown on the terminal.

The intuitive outcome from that code would be the substring alifo as the index 1 corresponds to a inside the string and 5 corresponds to o. However, the right side of the brackets will actually say where the slicing have to stop rather than where does the substring, resulting in the substring alif as shows the illustration below.

Python String Example

What if we put negative numbers inside the brackets?

If just one negative number is passed inside the brackets the slicing will then start backwards, towards the start of the string where -1 represents the last character, -2 the next-to-last and so on.

find()

The method find() allows us to find the index of a matched substring inside strings that we pass as a parameter inside the function.

title = 'Welcome to our website!'

has_welcome = title.find('Welcome')

The variable has_welcome will receive zero as it’s value because find() will either return the index of the first character of our substring parameter within the string if it occurs or -1 if the former case were not satisfied.

replace()

This method will replace matched occurrences (if there are any) within strings and return a new value containing the original string and the replacements were made.

title = 'Welcome to our website!'

replace_welcome = title.replace('Welcome', 'Be welcome')

Our variable replace_welcome will receive the value Be welcome to our website! as replace() found a match for the substring we passed as argument; The outcome would have been the original string if our substring had not matched any part of the string.

Notice that replace() is also case sensitive and will produce different outcomes based on minimal details within the string.

len()

Will return the total length of the string as a integer and the integer 0 if the string is empty.

store = "Walmart"

print(len(store))

The terminal will print 7 which is the total length of our string store.

This method, as for many other built-in functions that work in strings, works for lists as well returning the total number of elements within the list and 0 if there are none.