How do I check if a variable exists?

Going beyond try-except: considering scope and attributes

Checking within the local and global scopes

Not all variables are created equal. Some exist in the local scope, while others in the global one. Like at a party: some people are in the kitchen, some in the living room.

• Local scope: Check for local variables with if 'variable_name' in locals():. It's like rifling through your own pockets for keys.
• Global scope: For globally available variables, use if 'variable_name' in globals():. This effectively scours the entire party venue looking for 'Alex'.

Checking object attributes

Working with objects? Cool! You can be a sleuth and check if an attribute exists:

if hasattr(some_object, 'attribute_name'):
    print("Eureka! The attribute exists!")
else:
    print("This attribute is like my will to work out. Non-existent.")


Now who said programming can't be fun?

Initialization practices

As a rule of thumb, initialize your variables. Treat them like guests at a party, always offering them a drink (None).

• Use None as a sentinel. Then you can check if variable is not None like counting the empty glasses at the end of the night.
• Counters or tally markers are best set off at 0 because trust me, you don't want to start a count from a non-zero number. It's as good as shooting yourself in the foot.

Advanced techniques to check variable existence

Introducing 😎 cool ideas to make your variable checks more robust:

Effective programming practices with variables

• As a best practice, always initialize your variables. It avoids surprises and random jump scares from lurking NameErrors.
• Setting the variables to None or an appropriate default helps the people reading your code understand its intent better.

Checking variable attributes sans errors

• Use the 'var' in dir(obj) syntax to safely check attributes, without exceptions looming overhead. Much like wearing safety goggles in a chemistry lab.
• And please... for sanity's sake, try to avoid declaring global variables wherever possible.

Exception handling done right

• In Python, the try-except mechanism is your safety helmet, not your primary mode of transport. Use it judiciously but don't rely on it for everything.
• And when you do use it, handle the NameError so you can assign default values as necessary. Like a backup generator kicking in when the power goes off.