How to Use str.find in pandas for String Search

In pandas, use Series.str.find(substring) to find the position of a substring in each string of a Series. It returns the lowest index where the substring is found or -1 if not found.

Syntax

The str.find() method is used on a pandas Series containing strings. It searches for a substring and returns the lowest index of its occurrence.

• substring: The string you want to find.
• Returns: Integer position of the substring or -1 if not found.

python

Series.str.find(substring)

Example

This example shows how to find the position of the substring 'cat' in each string of a pandas Series. If 'cat' is not found, it returns -1.

python

import pandas as pd

# Create a Series of strings
animals = pd.Series(['cat', 'dog', 'caterpillar', 'bird'])

# Find the position of substring 'cat'
positions = animals.str.find('cat')
print(positions)

Output

0    0
1   -1
2    0
3   -1
dtype: int64

Common Pitfalls

One common mistake is expecting str.find() to return a boolean indicating presence. Instead, it returns the index or -1. To check presence, compare the result to -1.

Also, str.find() works only on string data; non-string values may cause errors or unexpected results.

python

import pandas as pd

# Wrong way: expecting boolean
animals = pd.Series(['cat', 'dog', 'caterpillar', 'bird'])
result_wrong = animals.str.find('cat')
print(result_wrong == True)  # Incorrect check

# Right way: check if found (index >= 0)
result_right = animals.str.find('cat') >= 0
print(result_right)

Output

0    False
1    False
2    False
3    False
dtype: bool
0     True
1    False
2     True
3    False
dtype: bool

Quick Reference

Method	Description	Return Type
str.find(substring)	Find lowest index of substring	int (index or -1)
str.contains(substring)	Check if substring exists	bool
str.index(substring)	Find lowest index, error if not found	int

Key Takeaways

Use Series.str.find(substring) to get the index of a substring or -1 if missing.

Check if substring exists by comparing find result to -1, not by boolean conversion.

str.find works only on string data; non-string values may cause errors.

For boolean presence, consider using Series.str.contains instead.

str.find returns the first occurrence index, useful for locating substrings.