str.contains() for pattern matching in Pandas - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of str.contains() with case sensitivity

What is the output of the following code snippet?

Pandas

import pandas as pd

df = pd.DataFrame({'text': ['Apple', 'banana', 'Cherry', 'date']})
result = df['text'].str.contains('a')
print(result.tolist())

A [false, true, false, true]

B [true, true, true, true]

C [true, true, false, true]

D [true, false, false, true]

💡 Hint

Remember that str.contains() is case sensitive by default.

The pattern 'a' matches only lowercase 'a'. 'Apple' has uppercase 'A' so false, 'banana' true, 'Cherry' false, 'date' true. So the result is [false, true, false, true].

❓ data_output

intermediate

Filter rows using str.contains() with regex

Given the DataFrame below, which rows remain after filtering with str.contains('^b.*a$', regex=true)?

Pandas

import pandas as pd

df = pd.DataFrame({'words': ['banana', 'beta', 'bat', 'boa', 'baba', 'cab']})
filtered = df[df['words'].str.contains('^b.*a$', regex=True)]
print(filtered['words'].tolist())

A ['banana', 'beta', 'baba']

B ['banana', 'beta', 'bat', 'baba']

C ['banana', 'beta', 'baba', 'bat', 'boa']

D ['banana', 'beta', 'boa', 'baba']

💡 Hint

The regex '^b.*a$' means strings starting with 'b' and ending with 'a'.

'banana', 'beta', 'boa', 'baba' start with 'b' and end with 'a'. 'bat' ends with 't', 'cab' starts with 'c'. The output preserves order: ['banana', 'beta', 'boa', 'baba'].

🔧 Debug

advanced

Identify the error in str.contains() usage

What error does the following code raise?

Pandas

import pandas as pd

df = pd.DataFrame({'col': ['abc', 'def', 'ghi']})
result = df['col'].str.contains(123)
print(result)

A TypeError: expected string or bytes-like object

B ValueError: invalid regex pattern

C AttributeError: 'int' object has no attribute 'contains'

D No error, outputs a boolean Series

💡 Hint

Check the type of the pattern argument passed to str.contains().

str.contains() expects a string or regex pattern. Passing an integer causes a TypeError.

🚀 Application

advanced

Use str.contains() to find rows with multiple patterns

You want to filter rows where the 'text' column contains either 'cat' or 'dog'. Which code correctly does this?

Pandas

import pandas as pd

df = pd.DataFrame({'text': ['catfish', 'dogma', 'bird', 'catalog', 'frog']})

A df[df['text'].str.contains('cat&dog')]

B df[df['text'].str.contains('cat|dog')]

C df[df['text'].str.contains(['cat', 'dog'])]

D df[df['text'].str.contains('cat,dog')]

💡 Hint

Use regex OR operator '|' inside the pattern string.

Option B uses regex 'cat|dog' which matches strings containing 'cat' or 'dog'. Other options are invalid or do not work as intended.

🧠 Conceptual

expert

Understanding na parameter in str.contains()

What is the output of the following code?

Pandas

import pandas as pd
import numpy as np

df = pd.DataFrame({'text': ['apple', np.nan, 'banana', np.nan]})
result = df['text'].str.contains('a', na=False)
print(result.tolist())

A [true, true, true, true]

B [true, true, false, false]

C [true, false, true, false]

D [true, false, true, true]

💡 Hint

The na parameter controls the output for missing values.

With na=False, missing values (NaN) are treated as false in the output boolean Series.