Import statement behavior in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the import statement do in Python?

It loads a module so you can use its functions, classes, or variables in your code.

intermediate

What happens if you import the same module multiple times in Python?

Python loads the module only once and reuses it, so importing again does not reload the module.

beginner

Explain the difference between <code>import module</code> and <code>from module import name</code>.

<code>import module</code> imports the whole module and you access items with <code>module.name</code>. <br><code>from module import name</code> imports only the specific item directly, so you use <code>name</code> without the module prefix.

beginner

What is the effect of using <code>import module as alias</code>?

It imports the module but lets you use a shorter or different name (alias) to refer to it in your code.

intermediate

How does Python find the module when you use an import statement?

Python looks in a list of places called sys.path, which includes the current folder, installed packages, and standard library folders.

What will happen if you write import math twice in the same Python program?

A Python ignores the second import statement.

B The math module is loaded twice, causing an error.

C The second import overwrites the first one.

D The math module is loaded only once and reused.

Python loads a module only once per program run and reuses it for subsequent imports.

Which import style allows you to use a function directly without the module name?

A from module import function

B import module as alias

C import module

D import *

Using from module import function lets you call function() directly.

What does import module as alias do?

A Imports only the alias from the module.

B Imports the module and renames it to alias.

C Imports the module twice.

D Creates a new module named alias.

It imports the module but lets you use the shorter name alias in your code.

Where does Python look for modules when you use an import statement?

A Only in the standard library.

B Only in the current folder.

C In the current folder, installed packages, and standard library folders.

D Only in the internet.

Python searches a list of folders called sys.path, including current folder and installed packages.

What happens if you try to import a module that does not exist?

A Python raises a ModuleNotFoundError.

B Python creates a new empty module.

C Python ignores the import.

D Python imports a default module instead.

Python raises an error called ModuleNotFoundError if the module cannot be found.

Explain how Python handles multiple imports of the same module in a program.

Think about efficiency and how Python avoids repeating work.

Describe the difference between import module and from module import name in Python.

Consider how you write the code after importing.

Practice

1. What happens when you use import module_name in Python?

easy

A. The module is copied into your current file.

B. Only the functions you call from the module are loaded.

C. The module code runs every time you call a function from it.

D. The entire module is loaded and its code runs once.

Solution

1. Step 1: Understand import behavior

   When you import a module, Python loads the whole module and runs its code once.

2. Step 2: Recognize module reuse

   After the first import, Python reuses the loaded module without running its code again.

3. Final Answer:

   The entire module is loaded and its code runs once. -> Option D

4. Quick Check:

   Import runs module once = A [OK]

Hint: Import runs module code once, then reuses it [OK]

Common Mistakes:

• Thinking module code runs every time a function is called
• Believing only used functions are loaded
• Assuming module code is copied into current file

2. Which of the following is the correct syntax to import only the sqrt function from the math module?

easy

A. from math import sqrt

B. import math.sqrt

C. import sqrt from math

D. from sqrt import math

Solution

1. Step 1: Recall import syntax for specific functions

   To import a specific function, use from module import function.

2. Step 2: Match syntax to options

   from math import sqrt matches this syntax: from math import sqrt.

3. Final Answer:

   from math import sqrt -> Option A

4. Quick Check:

   Specific import uses 'from module import item' = A [OK]

Hint: Use 'from module import name' to import parts [OK]

Common Mistakes:

• Using dot notation in import statement incorrectly
• Swapping module and function names
• Using 'import' with 'from' in wrong order

3. Consider two files:

# file1.py print('Loading file1') value = 10
# file2.py import file1 import file1 print(file1.value)

What is the output when running file2.py?

medium

A. Loading file1
Loading file1
10

B. Loading file1
10

C. 10
10

D. Error: module imported twice

Solution

1. Step 1: Understand module import behavior

   Python runs the module code only once, even if imported multiple times.

2. Step 2: Trace the output

   On first import, 'Loading file1' prints. Second import does nothing. Then prints value 10.

3. Final Answer:

   Loading file1 10 -> Option B

4. Quick Check:

   Module code runs once, reused later = B [OK]

Hint: Module code runs once, even if imported multiple times [OK]

Common Mistakes:

• Expecting module code to run twice
• Thinking repeated imports cause errors
• Confusing print output order

4. What is wrong with this code?

import math from math import sqrt print(math.sqrt(16))

medium

A. You cannot import the same module twice.

B. The code will cause a NameError.

C. There is no error; the code runs and prints 4.0.

D. You must use only one import style per module.

Solution

1. Step 1: Check import statements

   Importing the same module twice with different styles is allowed and does not cause error.

2. Step 2: Verify function call

   Calling math.sqrt(16) works and returns 4.0.

3. Final Answer:

   There is no error; the code runs and prints 4.0. -> Option C

4. Quick Check:

   Multiple imports allowed; function call works = D [OK]

Hint: Multiple imports of same module are allowed [OK]

Common Mistakes:

• Thinking multiple imports cause errors
• Confusing import styles must be exclusive
• Expecting NameError from this code

5. You have a module config.py with a variable setting = 5. In your main program, you do:

import config config.setting = 10 import config print(config.setting)

What will be printed and why?

hard

A. 10, because the module is loaded once and changes persist.

B. Error, because you cannot assign to module variables.

C. 5, because the second import reloads the module resetting variables.

D. None, because the variable is not accessible after import.

Solution

1. Step 1: Understand module import caching

   Python loads a module once and caches it; subsequent imports reuse the same module object.

2. Step 2: Analyze variable assignment and import

   Changing config.setting to 10 modifies the cached module. The second import does not reload, so the change remains.

3. Final Answer:

   10, because the module is loaded once and changes persist. -> Option A

4. Quick Check:

   Module cached; changes persist = C [OK]

Hint: Module imports cache; variable changes stay across imports [OK]

Common Mistakes:

• Assuming second import reloads module
• Thinking module variables are immutable
• Believing variable becomes inaccessible