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# Finding Strings in Python: Examples with find() and rfind() functions

# Example string
phrase = "A sunny day, reading under the tree."

# Using find() function: find a specific string from the beginning
tree_position = phrase.find("tree")

print("tree_position:", tree_position)  # 29

# Using rfind() function: find a specific string from the end
sun_position = phrase.rfind("sunny")

print("sun_position:", sun_position)  # 2

# Using find() to search for a non-existent string
not_found_position = phrase.find("rain")

print("not_found_position:", not_found_position)  # -1

# Using rfind() to search for a non-existent string
not_found_position_rfind = phrase.rfind("rain")

print("not_found_position_rfind:", not_found_position_rfind)  # -1

# Using find() function to search for a specific character
day_position = phrase.find("day")

print("day_position:", day_position)  # 7

# Finding the Position of a Specific Character Using find() and rfind()

How would you find which position the character `"a"` is in within the string `"banana"`?

The `find()` and `rfind()` functions locate the position of a specific character or substring within a string.

<br />

## How to Use the find() Function

The `find()` function searches for a specified character or substring from the beginning (left) of the string and returns the index number of its starting position.

> *What is an index?* : In programming, an index refers to a number representing the order. In a string composed of multiple characters, each character has an index, and it starts from 0. For example, in the string `"hello"`, the index of `"h"` is 0, and the index of `"e"` is 1.

Spaces in a string are also counted as part of the index. If the substring appears multiple times, the `find()` function returns the index of its first occurrence.

If the character or substring does not exist in the string, it returns `-1`.

```python title="Example Usage of find()"
text = "Python class, class is fun"

# Return the starting position of "class" from the beginning of the text string
position = text.find("class")

# Return the starting position of the first occurrence of "class" from the left
print(position)
```

In the string `"Python class, class is fun"`, each character is assigned an index as follows:

```plaintext title="String Index"
0: 'P'
1: 'y'
2: 't'
3: 'h'
4: 'o'
5: 'n'
6: ' '
7: 'c'
8: 'l'
9: 'a'
10: 's'
...
```

In the code above, the `find()` function searches for the substring `"class"` in the string `text` from the left.

The substring `"class"` begins at the 7th index, so the `find()` function returns `7`, the start position of `"class"`.

<br />

## How to Use the rfind() Function

The `rfind()` function searches for a specified character or substring starting from the right (end) of the string and returns its index.

If the character or substring is not found, it returns `-1`.

```python title="Example Usage of rfind()"
text = "Python class, class is fun"

# Return the starting position of "class" from the end of the text string
position = text.rfind("class")

# Return the starting position of the first occurrence of "class" from the right
print(position)
```

The `rfind()` function searches for the substring `"class"` in the string `text` from the right.

The substring `"class"` starts at the 14th index, so the `rfind()` function returns `14`, the start position when searched from the right.

The rfind() function searches for a substring starting from the end (right) of the string and returns the index. If the substring is not found, it returns -1.

The rfind() function searches for a substring from the beginning (left) of the string but returns the index of the last occurrence.