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.

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

1.2 Data type conversion functions

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

<code>>> 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]'
</code>

1.3 Numeric conversion functions

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

<code>>> 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)
</code>

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 .

<code>>> 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]
</code>

1.5 help

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

<code>help(range)
</code>

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.

<code>def func_name(param1, param2, ...):
    statement1
    statement2
    return result
</code>

Example of a quadratic function:

<code>def func1(x):
    return x**2 + 2*x + 3
</code>

Example of a function computing triangle area:

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

Calling the functions:

<code>>> func1(3)
18
>>> area(3,6)
9
</code>

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

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

Calling with and without the default:

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

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