How to Use str.len in pandas to Get String Lengths

Use Series.str.len() in pandas to get the length of each string element in a Series or DataFrame column. It returns a new Series with the count of characters for each string, handling missing values safely.

Syntax

The basic syntax to get string lengths in pandas is:

Series.str.len()

Here:

• Series is a pandas Series containing string values.
• str accesses string methods for the Series.
• len() returns the length of each string element.

python

series.str.len()

Example

This example shows how to use str.len() on a pandas Series to find the length of each string:

python

import pandas as pd

# Create a Series with string values
series = pd.Series(['apple', 'banana', 'kiwi', None, 'orange'])

# Get length of each string
lengths = series.str.len()

print(lengths)

Output

0    5
1    6
2    4
3    NaN
4    6
dtype: object

Common Pitfalls

Common mistakes when using str.len() include:

• Applying str.len() on non-string data without converting, which causes errors.
• Not handling NaN or None values, which return NaN in the result.
• Trying to use len() directly on a Series instead of str.len().

Correct usage ensures safe handling of missing values and works only on string data.

python

import pandas as pd

# Wrong: Using len() on Series (raises error)
# series = pd.Series(['a', 'bb', 'ccc'])
# lengths = len(series)  # This returns total length of Series, not string lengths

# Right: Use str.len()
series = pd.Series(['a', 'bb', 'ccc', None])
lengths = series.str.len()
print(lengths)

Output

0    1
1    2
2    3
3    NaN
dtype: object

Quick Reference

Method	Description	Example Output
str.len()	Returns length of each string element	[5, 6, 4, NaN, 6]
str.upper()	Converts strings to uppercase	['APPLE', 'BANANA', 'KIWI', NaN, 'ORANGE']
str.lower()	Converts strings to lowercase	['apple', 'banana', 'kiwi', NaN, 'orange']
str.strip()	Removes whitespace from ends	['apple', 'banana', 'kiwi', NaN, 'orange']

Key Takeaways

Use Series.str.len() to get the length of each string in a pandas Series.

str.len() safely handles missing values by returning NaN for them.

Do not use Python's len() on a Series to get string lengths; it returns the Series length instead.

Ensure your Series contains strings or convert data before using str.len().

str.len() is a quick way to analyze string length distributions in your data.