What are __signature__ and __text_signature__ used for in Python

What are __signature__ and __text_signature__ used for in Python

__signature__ and __text_signature__ are attributes that are used in Python to provide information about the function signature of callable objects, such as functions and methods. These attributes are part of the Python's inspect module, which is used for introspecting and examining objects in Python.

  • __signature__:

__signature__ is an attribute that holds an instance of the inspect.Signature class, which represents the parameters and their annotations of a callable object. This attribute allows you to programmatically inspect the signature of a function or method, retrieve parameter names, default values, annotations, and more. You can use it to access and analyze the function's signature programmatically.

Here's a simple example:

import inspect

def example_function(a, b=10, *args, **kwargs):
    pass

signature = inspect.signature(example_function)
print(signature.parameters)
  • __text_signature__:

__text_signature__ is a special attribute that is used by some built-in Python functions and methods to provide a concise human-readable representation of the function's signature. It is a string that describes the function's parameters and their types. This attribute is used mainly for documentation purposes and is not meant to be programmatically manipulated like __signature__.

Here's an example of __text_signature__ usage with the built-in map() function:

>>> map.__text_signature__
'(func, *iterables, /)'

In this example, the __text_signature__ attribute tells you that the map() function takes a required func argument and any number of iterable arguments.

Overall, both __signature__ and __text_signature__ are related to function signatures and introspection, but they serve different purposes. __signature__ is used for programmatic introspection, while __text_signature__ provides a human-readable description of the signature for documentation.

Examples

  1. What are signature and text_signature attributes in Python?

    • __signature__ and __text_signature__ are special attributes in Python used for introspection of functions and methods. They provide information about the function's signature, including parameter names, types, and default values.
    def my_function(a, b=10):
    return a + b

signature = my_function.__signature__
text_signature = my_function.__text_signature__

print(signature)  # Output: (a, b=10)
print(text_signature)  # Output: (a, b=10)

  2. How to access function signature in Python using signature attribute?

    • The __signature__ attribute of a function provides access to its signature as a inspect.Signature object, which can be used to extract information about parameters, return types, etc.
    import inspect

def my_function(a, b=10):
    return a + b

signature = inspect.signature(my_function)
print(signature)  # Output: (a, b=10)

  3. What is the purpose of text_signature attribute in Python?

    • The __text_signature__ attribute provides a string representation of a function's signature, suitable for display purposes or documentation generation.
    def my_function(a, b=10):
    return a + b

text_signature = my_function.__text_signature__
print(text_signature)  # Output: (a, b=10)

  4. How to retrieve a function's signature as a string using text_signature in Python?

    • The __text_signature__ attribute of a function provides a string representation of its signature, including parameter names and default values.
    def my_function(a, b=10):
    return a + b

text_signature = my_function.__text_signature__
print(text_signature)  # Output: (a, b=10)

  5. Can signature attribute be used to modify function signature in Python?

    • No, the __signature__ attribute is read-only and cannot be used to modify a function's signature.
    def my_function(a, b=10):
    return a + b

my_function.__signature__ = None  # Raises AttributeError

  6. How to extract parameter information from a function's signature using signature attribute?

    • You can extract parameter information from a function's signature using the parameters attribute of its __signature__ object.
    import inspect

def my_function(a, b=10):
    return a + b

signature = inspect.signature(my_function)
parameters = signature.parameters

for param_name, param_info in parameters.items():
    print(param_name, param_info.default)

  7. What does the text_signature attribute contain for a function with no parameters in Python?

    • For a function with no parameters, the __text_signature__ attribute contains an empty string.
    def my_function():
    return 0

text_signature = my_function.__text_signature__
print(text_signature)  # Output: ""

  8. How to generate a function signature string from signature attribute in Python?

    • You can generate a function signature string from its __signature__ attribute using the str() function on the signature object.
    import inspect

def my_function(a, b=10):
    return a + b

signature = inspect.signature(my_function)
signature_str = str(signature)

print(signature_str)  # Output: (a, b=10)

  9. **What does text_signature attribute contain for a function with *args and kwargs in Python?

    • For a function with *args and **kwargs parameters, the __text_signature__ attribute contains the string representation of these parameters.
    def my_function(*args, **kwargs):
    return sum(args)

text_signature = my_function.__text_signature__
print(text_signature)  # Output: (*args, **kwargs)

  10. How to access the return annotation of a function using signature attribute in Python?

    • You can access the return annotation of a function using the return_annotation attribute of its __signature__ object.
    import inspect

def my_function(a: int, b: int) -> int:
    return a + b

signature = inspect.signature(my_function)
return_annotation = signature.return_annotation

print(return_annotation)  # Output: <class 'int'>

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