Python Modules and Imports

A problem you can recognise

You need a square root in your program. Writing an approximate replacement before checking the standard library would create unnecessary work and new opportunities for errors. Importing a module lets you use an existing implementation while keeping its origin visible.

However, importing a name does not mean that every package mentioned on the internet is already installed or available in this browser runtime. We will keep those boundaries explicit.

Understand the idea

A module provides a namespace that groups related definitions. Importing a module binds a name through which you can access its members. Using math.isqrt makes both the operation and its source visible; importing one selected name can be convenient when that name remains unambiguous in the surrounding code.

The standard library ships with Python, but availability still depends on the execution environment. Browser practice is not an unrestricted operating-system shell. Do not assume that every standard-library feature can access files, spawn processes or contact networks here. Third-party packages are not automatically available just because an example on the internet imports them.

Avoid wildcard imports in introductory application code because they hide where names came from and can overwrite existing bindings. Do not name your own source file math.py or json.py when you intend to import the standard-library module of that name: local naming conflicts can produce confusing behaviour. Imports can execute module-level code, so shared modules should avoid unexpected work at import time. A main guard lets a module distinguish direct execution from being imported by another program.

Example 1: Use a module namespace

import math
print(math.isqrt(81))
print(math.ceil(2.2))

Expected output:

9
3

isqrt gives the integer square root, and ceil rounds upward to an integer. Prefixing both names with math makes their origin explicit.

Example 2: Import one selected name

from math import gcd
print(gcd(18, 24))

Expected output:

6

gcd becomes a name in the current namespace. This is not the same spelling as importing math and then calling math.gcd, although both access the same standard-library operation.

Example 3: Inspect a familiar namespace

import string
print(string.ascii_lowercase[:3])
print(string.digits)

Expected output:

abc
0123456789

The module also exposes useful constant values, not only functions. The slice uses the same stop-excluded rule already studied for strings.

Think through the important decisions

With import math, the name math refers to the module, and math.sqrt identifies a function through that namespace. The dotted form helps a reader see where the function came from. A from-import brings a chosen name directly into the current namespace, which is convenient but makes naming conflicts worth considering.

Importing and calling are different actions. Making the function available does not perform your particular calculation. Trace the argument supplied by your call and inspect its result separately from the import statement.

Modules are also an organisation tool for your own code, but examples split across real files need an environment that can locate those files. This browser course does not promise arbitrary package installation, unrestricted network access or permanent filesystem storage. Use the supported built-in modules for these exercises and distinguish language knowledge from deployment capabilities.

Check the reasoning

Importing a module provides a namespace; it does not make every external package or system capability available.

A matching screenshot or output is one check, not proof that a program is correct for all inputs. Change one input, predict the new result and run again. If the result differs, find the first instruction where your prediction stops matching the program state. Keep that small case as a regression check when you fix the cause.

The mistake worth understanding

Naming your own local file math.py can shadow the standard-library module in environments that search that location first. Wildcard imports can also make a name's origin difficult to trace. Prefer an explicit import you can explain when debugging an unfamiliar program.

Independent practice

Use math.isqrt on three perfect squares and math.gcd on two positive integers. Keep module-qualified names in one version, then demonstrate a selected-name import in another. Explain the naming trade-off.

Practice hint

Use only the standard-library operations shown. No package installation or network access is needed.

Try a different case

For each imported name in the worked examples, state its origin and the operation your code actually calls. Then explain whether a proposed third-party import needs an additional dependency rather than assuming the import statement will install it.