str.lower() and str.upper() in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the str.lower() method do in pandas?

It converts all characters in a string column of a pandas DataFrame or Series to lowercase letters.

beginner

How does str.upper() affect text data in pandas?

It changes all characters in a string column to uppercase letters, making the text all capitalized.

beginner

Example: What will df['Name'].str.lower() do if df['Name'] contains ['Alice', 'BOB', 'Charlie']?

It will return a Series with ['alice', 'bob', 'charlie'], converting all names to lowercase.

intermediate

Can str.lower() and str.upper() be used on non-string columns in pandas?

No, these methods only work on string columns. Non-string columns must be converted to strings first.

beginner

Why might you want to use str.lower() or str.upper() in data cleaning?

To standardize text data so that comparisons and searches are case-insensitive and consistent.

What does df['City'].str.upper() do in pandas?

A Converts all city names to lowercase letters

B Converts all city names to uppercase letters

C Removes spaces from city names

D Splits city names into separate words

The str.upper() method converts all characters in the string column to uppercase.

If you want to make text comparisons case-insensitive, which method helps?

A str.lower()

B str.split()

C str.strip()

D str.replace()

Using str.lower() converts all text to lowercase, making comparisons ignore case differences.

What happens if you use str.upper() on a numeric column without converting it first?

A It raises an error because numbers are not strings

B It removes the numeric column

C It converts numbers to strings automatically

D It works and converts numbers to uppercase

The str.upper() method only works on string data; numeric columns must be converted first.

Which pandas attribute allows you to apply string methods like lower() and upper()?

A dt

B apply

C cat

D str

The str accessor is used to apply string methods on pandas Series or DataFrame columns.

What is the output of pd.Series(['Hi', 'Bye']).str.lower()?

A ['Hi', 'Bye']

B ['HI', 'BYE']

C ['hi', 'bye']

D Error

The str.lower() method converts all strings in the Series to lowercase.

Explain how and why you would use str.lower() and str.upper() in cleaning text data in pandas.

Think about making text uniform to avoid mismatches.

Describe what happens if you try to use str.upper() on a numeric column in pandas and how to fix it.

Consider data types and method compatibility.