NameError: name 'sys' is not defined in Python

NameError: name 'sys' is not defined in Python #

The Python "NameError: name 'sys' is not defined" occurs when we use the sys module without importing it first. To solve the error, import the sys module before using it - import sys.

Here is an example of how the error occurs.

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print('before')

# ⛔️ NameError: name 'sys' is not defined
print(sys.version)

print(sys.exit())

print('after')

To solve the error, we have to import the sys module.

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# 👇️ import sys first
import sys

print('before')

print(sys.version)

print(sys.exit())

print('after')

Even though the sys module is in the Python standard library, we still have to import it before using it.

Also, make sure you haven't imported sys in a nested scope, e.g. a function. Import the module at the top level to be able to use it throughout your code.

An alternative to importing the entire sys module is to import only the functions and constants that your code uses.

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from sys import version, exit

print('before')

print(version)

print(exit())

print('after')

The example shows how to import the exit() function and the version constant from the sys module.

Instead of accessing the members on the module, e.g. sys.exit(), we now access them directly.

This should be your preferred approach because it makes your code easier to read.

Conversely, when we import specific functions, it is much easier to see which functions from the sys module are being used.

The sys module provides access to variables used by the Python interpreter and to functions that interact with the interpreter.

You can view all of the functions and constants the sys module provides by visiting the official docs.

Conclusion #

The Python "NameError: name 'sys' is not defined" occurs when we use the sys module without importing it first. To solve the error, import the sys module before using it - import sys.