Understanding Display of Keyword Arguments in pandas BusinessDay Object

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πŸ’‘ Problem Formulation: When working with pandas in Python, specifically with time series data, data analysts often need to define custom business day frequencies that consider holidays or weekends differently. Once a custom BusinessDay object is created, it can sometimes be necessary to display the range of keyword arguments that were applied to this object – for inspection, debugging or documentation purposes. This article focuses on how to programmatically reveal these details after the object’s instantiation.

Method 1: Using the __dict__ Attribute

Every Python object carries a built-in __dict__ attribute which stores all its attributes. For pandas’ BusinessDay object, this means we can inspect its dictionary to find the keyword arguments that were used to construct it.

Here’s an example:

from pandas.tseries.offsets import BusinessDay

# Create BusinessDay object with specific arguments
bday = BusinessDay(weekmask='Mon Tue Wed Thu Fri', holidays=['2022-01-01', '2022-12-25'])

# Display the keyword arguments
print(bday.__dict__)

Output:

{
    'n': 1,
    'normalize': False,
    'weekmask': 'Mon Tue Wed Thu Fri',
    'holidays': ['2022-01-01', '2022-12-25'],
    'calendar': None,
}

The code defines a BusinessDay object with custom workdays and holidays. Using the __dict__ property, it then prints out all the attributes of the bday object, including the keyword arguments passed during its creation.

Method 2: Introspection with the Inspector module

Python’s inspection functionality, available through the inspect module, can be leveraged to examine the members of objects such as a BusinessDay from pandas. By filtering out members that aren’t methods or functions, we can narrow down to the instance attributes which include our keyword arguments.

Here’s an example:

import inspect
from pandas.tseries.offsets import BusinessDay

# Create BusinessDay object
bday = BusinessDay(weekmask='Mon-Fri')

# Use inspect module to get members
attributes = inspect.getmembers(bday, lambda a: not(inspect.isroutine(a)))
keyword_args = {a[0]: a[1] for a in attributes if not(a[0].startswith('__') and a[0].endswith('__'))}

# Display keyword arguments
print(keyword_args)

Output:

{
    'n': 1,
    'normalize': False,
    'weekmask': 'Mon-Fri',
    'holidays': None,
    'calendar': None,
}

This snippet creates a BusinessDay object and uses the inspect module to get all its members that are attributes but not methods. It then filters out any built-in private attributes (those starting and ending with double underscores) to display the keyword arguments.

Method 3: Subclassing BusinessDay to Add a Display Method

One can extend the functionality of the BusinessDay object by subclassing it and adding a custom method to display its keyword arguments. This approach encapsulates the functionality directly within the new class.

Here’s an example:

from pandas.tseries.offsets import BusinessDay

class MyBusinessDay(BusinessDay):
    def display_kwargs(self):
        return {key: value for key, value in self.__dict__.items() if not key.startswith('_')}

# Create custom BusinessDay object
my_bday = MyBusinessDay(weekmask='Mon-Fri')

# Display the keyword arguments using the new method
print(my_bday.display_kwargs())

Output:

{
    'n': 1,
    'normalize': False,
    'weekmask': 'Mon-Fri',
    'holidays': None,
    'calendar': None,
}

In this example, we define a new class MyBusinessDay that inherits from pandas’ BusinessDay. It includes a new method display_kwargs() that returns a dictionary of its keyword arguments. Creating an instance of MyBusinessDay and calling our new method prints the information.

Bonus One-Liner Method 4: Using vars() Function

The vars() function in Python returns the __dict__ attribute of an object, which is a dictionary containing the object’s variables. It’s a direct and clean way to display the keyword arguments of a BusinessDay object.

Here’s an example:

from pandas.tseries.offsets import BusinessDay

# Initialize BusinessDay object
bday = BusinessDay(weekmask='Mon-Fri')

# Display keyword arguments using vars()
print(vars(bday))

Output:

{
    'n': 1,
    'normalize': False,
    'weekmask': 'Mon-Fri',
    'holidays': None,
    'calendar': None,
}

This simple code block utilizes vars() to obtain and print the dictionary containing all the attributes of the bday object.

Summary/Discussion

  • Method 1: Using __dict__ Attribute. Strengths: Direct access to the object’s internal dictionary; easy to use. Weaknesses: May expose private and built-in attributes.
  • Method 2: Introspection with Inspector module. Strengths: Detailed and part of Python’s standard library, allowing for more refined inspection. Weaknesses: Slightly more complex and verbose than other methods.
  • Method 3: Subclassing BusinessDay to Add a Display Method. Strengths: Encapsulates functionality within a subclass; promotes reusability. Weaknesses: Overhead of creating a new class; could be overkill for simple tasks.
  • Method 4: Using vars() Function. Strengths: Concise and straightforward approach to access the object’s attributes. Weaknesses: Similar to __dict__, can include private and built-in attributes not relevant to the user.