Data Science with Python Certification Introduction to Python for Data Science 4

Question 1

What is the difference between `df.loc[]` and `df.iloc[]` in pandas?

Accepted Answer

`loc` uses labels; `iloc` uses integer positions

Answer

`loc` is label-based indexing while `iloc` is strictly integer position-based, which matters when index labels are not sequential integers.

Question 2

Which method in pandas returns the number of missing values per column?

Accepted Answer

df.isna().sum()

Answer

`df.isna()` returns a boolean DataFrame and `.sum()` aggregates True values (NaN) per column.

Question 3

In Python, what does `*args` in a function signature allow?

Accepted Answer

Passing a variable number of positional arguments

Answer

`*args` collects any number of positional arguments passed to a function into a tuple.

Question 4

What does `np.nan == np.nan` evaluate to in Python?

Accepted Answer

False

Answer

By IEEE 754 standard, NaN is not equal to itself; use `np.isnan()` to test for NaN values.

Question 5

Which Python library provides the `train_test_split` function for splitting datasets?

Accepted Answer

sklearn.model_selection

Answer

`train_test_split` is part of scikit-learn's `model_selection` module and splits arrays into random train/test subsets.

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