Functions

Updated Oct 28, 2019 ·

Overview

If there's no existing module or package for a task, we can create our own function. This helps avoid writing long, repetitive code. A common rule is DRY (Don't Repeat Yourself).

• Useful for repeated tasks
• Simplifies complex syntax
• Makes code reusable

Defining a Function

To create a function, we use def, which stands for "define".

def my_function():
    print("Hello, world!")

Notes:

• Add parentheses () after the function name.
• Inside the parentheses, define the arguments.
• The function header ends with a colon :.

Naming a Function

Functions can have any name, but they should be short and descriptive.

def calculate_total():
    pass

Writing Function Code

The function body is indented and can have multiple lines.

def average(numbers):
    total = sum(numbers)
    count = len(numbers)
    return total / count

Using the Function

We call a function by using its name and passing arguments.

result = average([10, 20, 30])
print(result)  # Output: 20.0

Storing the Output

We can save the result in a variable for later use.

average_sales = average([100, 200, 300])
print(average_sales)  # Output: 200.0

Arguments

Function Arguments

Functions take arguments, which are values provided inside parentheses when calling a function. There are two main types: positional and keyword arguments.

• Positional arguments

  Provided in order, separated by commas. The function assigns them based on position.

  round(3.14159, 2)  # 3.14

• Keyword arguments

  Each argument is assigned using its name, making the function call clearer.

  round(number=3.14159, ndigits=2)  # 3.14

Default Arguments

Some functions have default arguments, meaning a value is already assigned if none is provided.

• Example with round()

  help(round)  

  Output shows ndigits=None, meaning if omitted, it rounds to an integer.

• Why use default arguments?

  • Reduces required inputs for common cases
  • Allows flexibility to override when needed

Modifying the average() Function

We update the function to include a keyword argument with a default value.

def average(values, rounded=False):  
    avg = sum(values) / len(values)  
    return round(avg, 2) if rounded else avg  

sales = [100, 200, 300]  

print(average(sales))          # 200.0  
print(average(sales, True))    # 200.00  

Note:

• Using positional arguments

  • average(sales, False)returns200.0`.
  • Omitting rounded gives the same result.

• Using keyword arguments

  • average(values=sales, rounded=True) returns 200.00.

Example: Rounding a Calculation

We can round results before returning them.

def average(numbers):
    return round(sum(numbers) / len(numbers), 2)

Functions return a result using return.

Example: Arguments with Default Values

This function replaces spaces with underscores and converts text to lowercase by default.

def clean_text(text, lower=True):
  if lower == False:
    clean_text = text.replace(" ", "_")
    return clean_text
  else:
    clean_text = text.replace(" ", "_")
    clean_text = clean_text.lower()
    return clean_text
  if remove != None:
    clean_text = text.replace(remove, "")
    clean_text = clean_text.lower()
    return clean_text
  else:
    clean_text = text.lower()
    return clean_text

To call the function:

clean_text("ThIs iS a DirTy sEntENCe")

Output:

'this_is_a_dirty_sentence'  

Example: Data Structure Converter

This function converts a collection into a list, set, or tuple based on the specified data_type. If no data_type is provided, it defaults to "list".

def convert_data_structure(data, data_type="list"):
  if data_type == "tuple":
    data = tuple(data)
  elif data_type == "set":
    data = set(data)
  else:
    data = list(data)
  return data

To call the function and store in a variable:

texts = convert_data_structure({"a", 1, "b", 2, "c", 3})
print(texts)
print(type(texts))

Since no data_type is provided, the function defaults to a list.

[1, 'a', 3, 2, 'b', 'c']
<class 'list'>

If data_type="set", the function returns a set:

texts = convert_data_structure({"a", 1, "b", 2, "c", 3}, "set")
print(texts)
print(type(texts))

Output:

{1, 'a', 3, 2, 'b', 'c'}
<class 'set'>  

Example: Check Disk and CPU Usage

Get the script here: Sample python scripts.

This Python script checks disk and CPU usage using the shutil and psutil modules:

• shutil: disk_usage() to return disk statistics (total, used, and free space).

• psutil: cpu_percent() function retrieves the current CPU usage percentage.

Make sure to install psutil first:

pip3 install psutil 

To run the script:

./check-disk-cpu-usage.py

If you encounter a "permission denied" error, it indicates the script lacks execute permissions. Fix this by updating the permissions:

sudo chmod +x check-disk-cpu-usage.py

Another way to run it is:

python3 check-disk-cpu-usage.py