Import statement behavior in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of importing a module with side effects

What is the output when running this code?

Python

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

A

4.0
4.0

B

3.141592653589793
3.141592653589793

C

3.141592653589793
4.0

D Error: module math cannot be imported twice

💡 Hint

Remember that importing a module twice does not reload it.

The math module is imported once. The second import does nothing. math.pi prints 3.141592653589793 and math.sqrt(16) prints 4.0.

❓ Predict Output

intermediate

Effect of import * on namespace

What is the output of this code?

Python

from math import *
print(sin(0))
print(cos(0))

A

sin
cos

B

0
0

C Error: sin is not defined

D

0.0
1.0

💡 Hint

import * brings all functions into current namespace.

sin(0) returns 0.0 and cos(0) returns 1.0 from the math module.

❓ Predict Output

advanced

Importing a module with circular dependency

Given two modules a.py and b.py where each imports the other, what error occurs when running a.py?

Python

a.py:
import b
x = 5

b.py:
import a
y = 10

A AttributeError: partially initialized module 'a' has no attribute 'x'

B No error, runs fine

C SyntaxError: circular import not allowed

D ImportError: cannot import name 'a' from 'b'

💡 Hint

Circular imports without accessing attributes during module initialization do not cause errors.

Python handles circular imports by providing the partially initialized module object. Since b.py does not access any attributes from a.py during its initialization, no AttributeError occurs, and the program runs fine.

❓ Predict Output

advanced

Effect of import aliasing on variable access

What is the output of this code?

Python

import math as m
print(m.sqrt(25))
print(math.sqrt(25))

A

5.0
NameError: name 'math' is not defined

B

5.0
5.0

C

NameError: name 'm' is not defined
5.0

D Error: cannot use alias and original name together

💡 Hint

Aliasing changes the module name in current scope.

math is not defined because it was imported as m. m.sqrt(25) prints 5.0 but math.sqrt(25) raises NameError.

🧠 Conceptual

expert

Understanding import caching behavior

Which statement best describes Python's import caching behavior?

A Modules are loaded once and cached in sys.modules for reuse.

B Modules cannot be imported more than once in a program.

C Modules are loaded from disk every time they are imported.

D Modules are reloaded automatically if their source code changes.

💡 Hint

Think about how Python avoids repeated work when importing.

Python loads a module once and stores it in sys.modules. Subsequent imports use the cached module, improving performance.

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