Master Python Built-in Functions and Custom Function Basics

1 Built-in Python Functions

Python includes several built‑in functions such as type, len, and sum that display data types, count elements, and compute sums. The article also introduces other commonly used functions.

1.1 round

The round function rounds a floating‑point number to a given number of decimal places.

>> round(2.555,2)  # round to two decimal places
2.56

1.2 Data type conversion functions

Functions list, tuple, dict, set, and str convert values to the respective types.

>> list('abcd')
['a', 'b', 'c', 'd']
>>> tuple([1,2,3,4])
(1, 2, 3, 4)
>>> dict([(1,2),(3,4)])
{1: 2, 3: 4}
>>> set('abcd')
{'a', 'b', 'c', 'd'}
>>> str([1,2,3])
'[1, 2, 3]'

1.3 Numeric conversion functions

Functions float, int, bool, and complex convert values to floating‑point, integer, boolean, and complex numbers.

>> float(2)
2.0
>>> int(3.56)  # truncate decimal part
3
>>> bool(2)    # any non‑zero is True
True
>>> bool(0)
False
>>> float('200')
200.0
>>> complex(3)
(3+0j)

1.4 sorted

The sorted function returns a new sorted list. It can sort in ascending order, descending order with reverse=True, or using a custom key such as abs.

>> sorted([1,4,3,2])
[1, 2, 3, 4]
>>> sorted([1,4,3,2], reverse=True)
[4, 3, 2, 1]
>>> sorted([2,-1,4,-3], key=abs)
[-1, 2, -3, 4]

1.5 help

The help function displays the documentation of a function or object, e.g., help(range).

help(range)

2 Custom Functions

Defining your own functions allows modular code reuse. The syntax is def function_name(parameters): followed by indented statements and an optional return value.

def func_name(param1, param2, ...):
    statement1
    statement2
    return result

Example of a quadratic function:

def func1(x):
    return x**2 + 2*x + 3

Example of a function computing triangle area:

def area(base, height):
    return 1/2 * base * height

Calling the functions:

>> func1(3)
18
>>> area(3,6)
9

Functions can have default arguments, which are used when the caller omits that parameter.

def area2(base, height=2):
    return 1/2 * base * height

Calling with and without the default:

>> area2(3,6)  # overrides default height
9
>>> area2(3)    # uses default height=2
3

Note: default arguments must follow non‑default positional arguments.