Installing & Importing NumPy

Before you can score runs you need to walk out to the crease. Before you can use NumPy you need to install it (once per Python environment) and import it (once per script or notebook).

Definition

Installing a package downloads it from PyPI (the Python Package Index) into your Python environment, using pip. Importing a package loads it into the current program's memory so its functions can be used. The NumPy community convention is to import it under the short alias np.

• pip — Python's package installer. It comes with Python.
• Environment — a particular Python installation (system Python, a virtual environment, a conda env). A package installed in one environment is not visible in another.
• Alias — a nickname given with as. import numpy as np lets you write np.array instead of numpy.array.

Syntax

# In a terminal / command prompt (not inside Python):
pip install numpy              # install the latest version
pip install --upgrade numpy    # upgrade an existing install
pip show numpy                 # show installed version and location

# In a Jupyter / Colab notebook cell:
%pip install numpy

# In your Python code:
import numpy as np             # the standard way
print(np.__version__)          # check the version

Note: Google Colab, Anaconda, Kaggle notebooks and this site's browser playground already include NumPy — you can skip the install step there and go straight to import numpy as np.

Example — import and check the version

import numpy as np
print(np.__version__)

2.4.6

How it works: np.__version__ is a plain string attribute. Your version may be different — any NumPy 2.x works for this course. If you see a 1.x version, some printing details differ (for example, NumPy 2 shows a scalar as np.int64(72) in a notebook, while NumPy 1 showed 72), so upgrading is recommended.

Why np?

Every tutorial, Stack Overflow answer, documentation page and library uses np. Using the same alias makes your code instantly readable to everyone.

Warning: from numpy import * replaces Python's built-in sum, max, min, abs, round and others with NumPy versions that behave slightly differently. This causes very confusing bugs.

Common errors and fixes

Common mistakes

• ❌ Typing pip install numpy inside a Python script or the >>> prompt. ✅ Run it in a terminal; in notebooks use %pip install numpy.
• ❌ Saving your practice file as numpy.py. ✅ Give it a different name like numpy_practice.py.
• ❌ Importing NumPy in the middle of a notebook and running cells out of order. ✅ Put import numpy as np in the very first cell and run it first.

Interview tip

Q: You installed NumPy but still get ModuleNotFoundError. Why? A: It was installed into a different Python environment from the one running your code (e.g. system Python vs a virtual environment or Jupyter kernel). Install with python -m pip install numpy using the same interpreter, or %pip install numpy inside the notebook.