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Python: Errors when working with variables

The order of instructions in code with variables is of great importance. That's why the variable must be defined before you use it for the first time. Below is an example of a mistake often made by beginners:

greeting = 'Father!'

Running the program above ends with the error NameError: name 'greeting' is not defined - this is a reference error. This means that the code uses a name (identifier) that hasn't yet been defined. This is stated in the text of the error itself: 'greeting' is not defined. In addition to incorrect ordering, when working with Python, you can also come across simple typos in the name of the variable. This happens both when the variable is used and when it's declared.

You can reduce the number of such errors if you use a properly configured editor. It warns of possible problems and highlights variables that are used without being declared.


Find an undeclared variable in the program and declare it by assigning the value 'Dragon' to it.

After running the program, the result on the screen should look like this:

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.


  • Variable a way to save information and name it for later use in code.

If you got stuck and don't know what to do, you can ask a question in our community