Python | Functions | Built-in Functions

Of course, Python comes with a lot of built-in functions. We used input() and print() already. Here are few commonly used built-in functions:

  • range() – It returns an iterable sequence
  • open() – It opens a file then returns the corresponding file object
  • sorted() – It sorts a list and returns the sorted list
  • help() – It invokes the help system built into Python
  • abs() – Returns the absolute value of a number

The range() function

The parameter you put in between parenthesis acts like a stop. For example let’s take a look at the following example:

for i in range(5):
	print(i)

It prints all the numbers from 0 to 5 (but not including 5).

Python range() function

If we use it with 2 parameters then we will have something like is shown below:

for i in range(2,5):
	print(i)

It starts printing at number 2 and it stops at 4. Number 5 is not printed.

Python range() function

If we use it with 3 parameters then we will have something like is shown below:

for i in range(2,10,3):
	print(i)

It starts printing with number 2, then prints 5 (which is 2+3 and is less than 10), then prints 8 (which is 5+3 and it is also less than 10). Then it stops printing since the next number would have been 11 and it is out of range.

Python range() function

So, in conclusion, the range() is a general tool that can be used in a variety of contexts. It is commonly used to generate indexes in a for loop but you can use it anywhere you need a series of integers.

>>>>>> list(range(5))
[0, 1, 2, 3, 4]
>>> list(range(11, 17))
[11, 12, 13, 14, 15, 16]
>>> list(range(-3, 3, -1))
[]
>>> list(range(3, -3, -1))
[3, 2, 1, 0, -1, -2]
>>> list(range(-3, 3, 1))
[-3, -2, -1, 0, 1, 2]

The range() is useful when used within for loops. It is a simple way to repeat an action a specific number of times.

Example:
To print three lines, use range() to generate the appropriate number of integers.

>>> for i in range(3):
...     print(i, ' developer')
... 
0  developer
1  developer
2  developer

The open() function

The open() function opens a file. Let’s modify the file hello.py as shown below:

print('The message with open()')

Open the terminal, go to the directory where the file is and type the following commands:

f = open(“hello.py”)
f.read(9)

This is what the terminal outputs:

Python open() function

It reads the first 9 characters. Of course, you can do many more things with the open() function.

The sorted() function

The sorted() function does what the name says, it sorts the items of a list for example.

>>> a = [5,3,4,2,1]
>>> print sorted(a)
[1, 2, 3, 4, 5]
>>> 

Python sorted() function

The help() function

The help() invokes the help system built into Python. Open the terminal and type python to start Python then type help(). This is what you get:

python help() function

The abs() function

The abs() function returns the absolute value of a number. The absolute value of a number is its distance on the numbers line from 0.

Open the terminal and type in the following command:

abs(-5)

The terminal will return 5 as you can see below.

Python abs() function

The are many more built in functions in Python that you can study and experiment with.

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