Potentially uninitialized local variable¶
ID: py/uninitialized-local-variable Kind: problem Security severity: Severity: error Precision: medium Tags: - reliability - correctness Query suites: - python-security-and-quality.qls
This local variable may be used before it is defined. If a variable is assigned to in a function and not explicitly declared
nonlocal then it is assumed to be a local variable. If it is used before it is defined then an
UnboundLocalError will be raised.
Review the code and consider the intended scope of the variable. Determine whether the variable should be global or local in scope. If a global variable is required then add a
global statement, or in Python 3 you can use a
nonlocal statement if the variable occurs in an enclosing function. Otherwise, ensure that the variable is defined before it is used.
The following code includes different functions that use variables.
test1() fails with an
UnboundLocalError because the local variable
var is used before it is initialized.
def test(): var = 1 def print_var(): print var # Use variable from outer scope print_var() print var def test1(): var = 2 def print_var(): print var # Attempt to use variable from local scope. var = 3 # Since this is not initialized yet, this results print_var() # in an UnboundLocalError print var def test2(): var = 2 def print_var(): var = 3 # Initialize local version of the variable print var # Use variable from local scope. print_var() # Note that this local variable "shadows" the variable from print var # outer scope which makes code more difficult to interpret. def test3(): var = 4 def print_var(): nonlocal var # Use non-local variable from outer scope. print var print_var() print var
Python Standard Library: Built-in Exceptions: UnboundLocalError.
Python Frequently Asked Questions: Why am I getting an UnboundLocalError when the variable has a value?.
Python Course: Global and Local Variables.