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Python

What is a ModuleNotFoundError?

← Errors

A ModuleNotFoundError is a subclass of ImportError raised when Python cannot locate a module at all. Unlike ImportError (which can also fire when a specific name inside a module is missing), this error means the entire module was not found on sys.path.

Why it happens

  • •The package is not installed in the active virtual environment.
  • •The script is running in a different Python environment than the one where the package was installed.
  • •A typo in the module name.
  • •A local file has the same name as a standard library module, shadowing it.

Examples

Python

Code that triggers the error

import pandas as pd

df = pd.read_csv("data.csv")

Error output

Traceback (most recent call last):
  File "app.py", line 1, in <module>
    import pandas as pd
ModuleNotFoundError: No module named 'pandas'

How to fix it

Activate the correct virtual environment and run pip install <package>. Verify which Python interpreter is active with python --version and which pip you are using with pip --version. Check for naming conflicts between your local files and standard library modules.

Fixed code

# Install the missing package first:
# pip install pandas

import pandas as pd

df = pd.read_csv("data.csv")
print(df.head())

Related errors

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