Python Function Tutorial – Part VII

Articles From: QuantInsti
Website: QuantInsti

See the previous installment in this series to catch up with Python functions with default arguments.

Python functions with variable length arguments

Let’s consider a scenario where we as developers aren’t sure about how many arguments a user will want to pass while calling a python function. For example, a function that takes floats or integers (irrespective of how many they are) as arguments and returns the sum of all of them. We can implement this scenario as shown below:

def sum_all(*args):
“””Sum all values in the *args.”””
# Initialize result to 0
result = 0
# Sum all values
for i in args:
result += i
# Return the result
return result

The flexible argument is written as * followed by the parameter name in the Python function definition. The parameter args preceded by * denotes that this parameter is of variable length. Python then unpacks it to a tuple of the same name args which will be available to use within the function. In the above example, we initialize the variable result to 0 which will hold the sum of all arguments. We then loop over the args to compute a sum and update the result with each iteration. Finally, we return the sum to the calling statement. The sum_all python function can be called with any number of arguments and it will add them all up as follows:

# Calling the sum_all function with arbitrary number of arguments.
print(sum_all(1, 2, 3, 4, 5))
# Output
# Calling with different numbers of arguments.
print(sum_all(15, 20, 6))
# Output

Here, *args is used as the parameter name (the shorthand for arguments), but we can use any valid identifier as the parameter name. It justs needs to be preceded by * to make it flexible in length. On the same lines, Python provides another flavor of flexible arguments which are preceded by double asterisk marks. When used ,they are unpacked to dictionaries (with the same name) by the interpreter and are available to use within the function. For example:

def info(**kwargs):
“””Print out key-value pairs in **kwargs.”””
# Run for loop to prints dictionary items
for key, value in kwargs.items():
print(key + ‘: ‘ + value)

Here, the parameter **kwargs are known as keywords arguments which will be converted into a dictionary of the same name. We then loop over it and print all keys and values. Again, it is totally valid to use an identifier other than kwargs as the parameter name. The info python function can be called as follows:

# Calling the function
print(info(ticker=’AAPL’, price=’146.83′, name=’Apple Inc.’, country=’US’))
# Output
ticker: AAPL
price: 146.83
name: Apple Inc.
country: US

That is all about the default and flexible arguments.

In the next installment, the author will discuss documentation string, DocStrings.

Visit for ready-to-use Python functions as applied in trading and data analysis.

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