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Python Function Tutorial – Part V

Posted April 3, 2020
Jay Parmar
QuantInsti

See Part IPart II , Part III and Part IV of this installment to learn more about Python functions.

Python functions with multiple arguments and a `return` statement

Both versions of the `greet` Python functions defined above were actually straightforward in terms of functionality that they perform. One more functionality that functions are capable of performing is to return a value to the calling statement using the keyword `return`. Consider a function that takes several parameters, performs some mathematical calculation on it and returns the output. For example:

# Function with two parameters ‘a’ and ‘b’
“””Computes the addition and returns the result.
It does not implement the print statement.”””
result = a + b # Computes addition
return result # Returns the result variable

This user defined function `add` takes two parameters `a` and `b`, sums them together and assigns its output to a variable `result` and ultimately returns the variable to calling statement as shown below:

x = 5
y =

We call the function `add` with two arguments `x` and `y` (as the function definition has two parameters) initialized with `5` and `6` respectively, and the addition returned by the function gets printed via the `print` statement as shown below:

The addition of 5 and 6 is 11.

Similarly, Python functions can also return multiple values based on the implementation. The following function demonstrates the same.

# Function definition
def upper_lower(x):
“””Returns the upper and lower version of the string.
The value must be a string, else it will result in an error.
This function does not implement any error handling mechanism.”””
upper = x.upper() # Convert x to upper string
lower = x.lower() # Convert x to lower string
return upper, lower # Return both variables upper and lower

The above `upper_lower` function takes one argument `x` (a string) and converts it to their upper and lower versions. Let us call it and see the output.

Note: The function upper_lower implicitly assumes to have a string as a parameter. Providing an integer or float value as an argument while calling will result in an error.

# Calling the function
upper, lower = upper_lower(‘Python’)
# Printing output
print(upper)
PYTHON
print(lower)
python

Here, the call to `upper_lower` function has been assigned to two variables `upper` and `lower` as the function returns two values which will be unpacked to each variable respectively and the same can be verified in the output shown above.

In the next installment, the author will discuss Python functions with default arguments.

Visit https://www.quantinsti.com/ for ready-to-use Python functions as applied in trading and data analysis.

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