Interpretation of method to check whether an object has a certain attribute in Python

Python checks whether an object has a certain attribute method

Technical background

In Python programming, you often encounter situations where you need to check whether an object has a certain property.

Direct access to non-existent properties will causeAttributeErrorException, in order to avoid program crashes, checks are required before using properties.

Implementation steps

Use hasattr() function

hasattr()Functions are used to check whether an object has the specified attribute.

• It accepts two parameters:
• Object and property name and return a boolean value.

Sample code:

class SomeClass:
    pass

a = SomeClass()

if hasattr(a, 'property'):
    print()
else:
    print("The object does not have this property")

Catch AttributeError exception

passtry-exceptBlock CaptureAttributeErrorExceptions can also achieve the purpose of checking whether the attribute exists.

Sample code:

class SomeClass:
    pass

a = SomeClass()

try:
    print()
except AttributeError:
    print("The object does not have this property")

Use getattr() function

getattr()Functions can provide a default value while obtaining attribute values. If the property does not exist, the default value will be returned.

Sample code:

class SomeClass:
    pass

a = SomeClass()

value = getattr(a, 'property', 'default value')
print(value)

Best Practices

• Probably the attribute exists: If the attribute is likely to exist, access it directly and pass ittry-exceptBlock CaptureAttributeErrorException, this may be more likely thanhasattr()Faster.
• Probably no attribute exists: If the attribute is likely not present, usehasattr()Functions can avoid falling into exception blocks multiple times and improve efficiency.
• Default value required: If you just want to get the value of the property and provide a default value when the property does not exist, usegetattr()Functions are the best choice.

Frequently Asked Questions

The difference between hasattr() and try-except

In Python,hasattr()Will catch all exceptions, not justAttributeError。

In Python 3.2 and later,hasattr()Capture onlyAttributeError. Therefore, in some cases,try-exceptBlocks may be safer.

Property check of dictionary object

For dictionary objects,hasattr()The function does not apply.

AvailableinOperator to check whether a key exists in the dictionary.

Sample code:

a = {'property': 'value'}

if 'property' in a:
    print(a['property'])
else:
    print("The key is not in the dictionary")

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.