Python determines whether a variable exists

Question

How does Python determine whether a variable exists?

if var:
    var_exists = True
    
if not var:
    var_exists = True

This way you can make a judgment before making a decision and report an error

Answer 1

Reference article: Several classic questions on the road to learning Python

Python determines whether a variable exists

Method 1: Use try: ... except NameError: ....

try:
    var
except NameError:
    var_exists = False
else:
    var_exists = True

Method 2: Use the two built-in functions locals() and globals().

locals() : Dictionary-based way to access local variables. The keys are variable names and the values ​​are variable values.
globals() : Dictionary-based way to access global variables. The keys are variable names and the values ​​are variable values.

var_exists = 'var' in locals() or 'var' in globals()