str.len() for string length in Pandas - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of str.len() on a pandas Series

What is the output of the following code snippet?

Pandas

import pandas as pd
s = pd.Series(['apple', 'banana', 'cherry', None])
result = s.str.len()
print(result)

A

0    5
1    6
2    6
3    None
dtype: object

B

0    5
1    6
2    6
3    0
dtype: int64

C

0    5.0
1    6.0
2    6.0
3    NaN
dtype: float64

D

0    5
1    6
2    6
3    NaN
dtype: float64

💡 Hint

Remember that missing values in pandas string operations usually result in NaN, not zero or None.

The str.len() method returns the length of each string in the Series. For missing values (None), it returns NaN. The dtype is float64 because NaN is a float.

❓ data_output

intermediate

Count of strings with length greater than 4

Given the Series below, what is the count of strings with length greater than 4?

Pandas

import pandas as pd
s = pd.Series(['dog', 'elephant', 'cat', 'lion', 'tiger', None])
count = (s.str.len() > 4).sum()
print(count)

A 2

B 3

C 4

D 5

💡 Hint

Check which strings have length more than 4 and remember None values are ignored in comparison.

'elephant' (8) and 'tiger' (5) have length > 4. 'lion' (4) does not. 'dog' (3), 'cat' (3), and None (NaN, False in comparison) do not. Count is 2.

❓ visualization

advanced

Plot string length distribution

You have a pandas Series of strings. Which code snippet correctly plots a histogram of string lengths?

Pandas

import pandas as pd
import matplotlib.pyplot as plt
s = pd.Series(['red', 'blue', 'green', 'yellow', 'purple', 'orange'])
# Fill in the missing code to plot histogram of string lengths

A

plt.hist(s.str.length())
plt.show()

B

plt.hist(s.len())
plt.show()

C

plt.hist(len(s))
plt.show()

D

plt.hist(s.str.len())
plt.show()

💡 Hint

Use the pandas string accessor to get lengths before plotting.

s.str.len() returns a Series of string lengths. plt.hist() can plot this numeric data. Other options are invalid because len() is not a pandas method or attribute.

🔧 Debug

advanced

Identify the error in string length calculation

What error will the following code raise?

Pandas

import pandas as pd
s = pd.Series(['a', 'bb', 'ccc'])
lengths = s.len()
print(lengths)

A AttributeError: 'Series' object has no attribute 'len'

B TypeError: 'Series' object is not callable

C No error, prints lengths

D ValueError: Length mismatch

💡 Hint

Check if 'len' is a direct method of Series or accessed differently.

The Series object does not have a 'len()' method. The correct way is to use s.str.len() to get string lengths.

🚀 Application

expert

Filter DataFrame rows by string length in a column

Given a DataFrame df with a column 'Name', which code correctly filters rows where the 'Name' length is exactly 5 characters?

Pandas

import pandas as pd
df = pd.DataFrame({'Name': ['Alice', 'Bob', 'Charlie', 'David', 'Eve']})
# Fill in the code to filter rows with Name length 5

A

filtered = df[df['Name'].apply(len) == 5]
print(filtered)

B

filtered = df[df['Name'].str.len() == 5]
print(filtered)

C

filtered = df[df['Name'].len() == 5]
print(filtered)

D

filtered = df[df['Name'].str.length() == 5]
print(filtered)

💡 Hint

Use the pandas string accessor for vectorized string length operations.

Option B uses the correct pandas string accessor str.len() to get lengths. Option B works but is slower because it uses apply with Python len. Options B and D are invalid methods.