String Indexing & Slicing

Looking inside a string

A string is just a sequence of characters.

Often, you only want a specific piece of that sequence. Maybe you want the first letter of a user's name, or you want to extract the year from the date "2025-10-31".

Python allows you to grab individual characters, or chunks of characters, using a system called indexing and slicing.

Zero-based indexing

Every character in a string has a numbered position, called its index.

However, computers start counting at 0, not 1.

python
word = "Python"
print(word[0])  # Output: P
print(word[1])  # Output: y
print(word[5])  # Output: n

In the word "Python", the P is at index 0, and the n is at index 5.

If you try to grab an index that doesn't exist, like word[10], Python will crash with an IndexError.

Negative indexing

What if you have a very long paragraph, and you just want the very last character?

Counting all the way from the beginning would be slow and annoying.

Python provides a clever shortcut: negative numbers count backward from the end.

python
word = "Python"
print(word[-1])  # Output: n (the last character)
print(word[-2])  # Output: o (the second to last character)

Negative indexing is incredibly useful because it works no matter how long the string is. string[-1] is always the last letter.

Grabbing chunks with slicing

If you want more than one character, you can "slice" the string.

You do this by providing a start and a stop index, separated by a colon :.

python
word = "Python"
print(word[0:3])  # Output: Pyt

Here is the most important rule about slicing: Python includes the start index, but excludes the stop index.

So 0:3 gives you index 0, 1, and 2. It stops right before hitting index 3.

Slicing shortcuts

If you are starting from the very beginning, you can leave the start index blank.

python
print(word[:4])  # Output: Pyth (From start up to index 4)

If you are going all the way to the end, you can leave the stop index blank.

python
print(word[2:])  # Output: thon (From index 2 to the end)

By combining these, word[:] actually gives you a full copy of the entire string!

Skipping characters with step

There is a third, optional number you can add to a slice: the step.

It tells Python how many characters to jump forward each time.

The full format is [start:stop:step].

python
alphabet = "ABCDEFGHIJ"
print(alphabet[0:10:2])  # Output: ACEGI

This starts at 0, stops at 10, and jumps by 2 characters at a time. It effectively grabs every other letter.

The ultimate shortcut: reversing a string

If you use a negative step, Python will walk backwards through the string.

This gives us one of Python's most famous and elegant tricks.

To completely reverse a string in Python, you slice it from beginning to end, with a step of -1.

python
text = "racecar"
reversed_text = text[::-1]
print(reversed_text)  # Output: racecar

What this lesson should give you

After this lesson, you should understand how to:

• grab a single character using its index number (like text[0])
• remember that Python starts counting at 0
• grab the last characters easily using negative indexes (like text[-1])
• slice out a chunk of text using [start:stop]
• understand that the stop index is excluded
• use the step parameter to skip characters or reverse strings

Indexing and slicing are not just for strings! You will use these exact same techniques when we learn about Lists later in the course.