Python 3: UnboundLocalError: local variable referenced before assignment [duplicate]

by

This is because, even though Var1 exists, you’re also using an assignment statement on the name Var1 inside of the function (Var1 -= 1 at the bottom line). Naturally, this creates a variable inside the function’s scope called Var1 (truthfully, a -= or += will only update (reassign) an existing variable, but for reasons unknown (likely consistency in this context), Python treats it as an assignment). The Python interpreter sees this at module load time and decides (correctly so) that the global scope’s Var1 should not be used inside the local scope, which leads to a problem when you try to reference the variable before it is locally assigned.

Using global variables, outside of necessity, is usually frowned upon by Python developers, because it leads to confusing and problematic code. However, if you’d like to use them to accomplish what your code is implying, you can simply add, inside the top of your function:

global Var1, Var2

This will tell Python that you do not intend to define a Var1 or Var2 variable inside the function’s local scope. The Python interpreter sees this at module load time and decides (correctly so) to look up any references to the aforementioned variables in the global scope.

Some Resources

  • the Python website has a great explanation for this common issue.
  • Python 3 offers a related nonlocal statement – check that out as well.

More Related Contents:

  1. Accessing class variables from a list comprehension in the class definition
  2. How can I change a global variable from within a function?
  3. except-clause deletes local variable
  4. Nested list comprehension scope
  5. Why do I get a `NameError` (or `UnboundLocalError`) from using a named exception after the `except` block?
  6. How do the scoping rules work with classes?
  7. How to add a label to all words in a file? [closed]
  8. How to provide a reproducible copy of your DataFrame with to_clipboard()
  9. Getting a map() to return a list in Python 3.x
  10. Python NameError: name is not defined
  11. Windows Scipy Install: No Lapack/Blas Resources Found
  12. How do I unescape HTML entities in a string in Python 3.1? [duplicate]
  13. Generate a random letter in Python
  14. Install opencv for Python 3.3
  15. Types that define `__eq__` are unhashable?
  16. operator.itemgetter or lambda
  17. Seeking from end of file throwing unsupported exception
  18. Python output to Console within Subprocess from the child scricpt
  19. building Python from source with zlib support
  20. Python 3.1.1 string to hex
  21. EOFError: EOF when reading a line
  22. pandas or python equivalent of tidyr complete
  23. How do I run python 2 and 3 in windows 7? [duplicate]
  24. Python type hinting with exceptions
  25. Is Python’s order of evaluation of function arguments and operands deterministic (+ where is it documented)?
  26. How to make a command case insensitive in discord.py
  27. How to tell if a string contains valid Python code
  28. Appending to list in Python dictionary [duplicate]
  29. Installing TensorFlow on Windows (Python 3.6.x)
  30. Weird MRO result when inheriting directly from typing.NamedTuple

Leave a Comment