Top Python Functions for Developers

In Python, a function is a group of statements written to fulfil specific tasks. Instead of duplicating the same code repeatedly when a block of code is required in multiple portions of a programme, programmers might simply write one block of code and use it anywhere they wish. Programs use functions to avoid redundancy and unneeded complexity. The Python standard library contains a wide range of functions, each integral to making the code more legible and efficient. Here’s a comprehensive list of the top Python functions for any developer to know.

Introduction to Python Functions

In Python, there are two types of functions:

  • User-defined functions
  • Built-in functions

User-defined functions are those that users develop and utilise. In contrast, built-in functions are already included in Python and can be used by programmers to obtain desired results quickly.

Here, we are going to look at the list of essential Python functions every developer knows of.

Python List Functions

The Python list functions are a collection of tasks that can be used to manipulate a list or an array. They are also referred to as array functions.

Here is the list of Python list functions:


Adds a single element to the list’s end.

Syntax: list.append(element)

Here, the element refers to a component of any type (string, number, object etc.)


All elements in the list are removed or cleared.

Syntax: list.clear()


This method returns a duplicate of the list.

Syntax: list.copy()


The number of elements with the given value is returned.

Syntax: list.count(value)


Add the elements of a list at the end of the list.

Syntax: list.extend(iterable)


The index of the first element with the specified value is returned.

Syntax: list.index(element)


Adds a new element to the specified location.

Syntax: list.insert(pos, element)


  • The pos specifies the location in which the element will be placed.
  • The element denotes the element that will be inserted.


Removes the element from the specified location.

Syntax: list.pop(position)


The first item with the provided value is removed.

Syntax: list.remove(element)


Reverses the list’s order.

Syntax: list.reverse()


Sorts the items in the list

Syntax: list.sort(reverse=True|False, key=myFunc)


  • If the items sort the list in ascending order, the list will be sorted in ascending order. If false, the list will stay the same.
  • The key refers to a function to specify the sorting criteria.

Python String Functions

A string in Python is a collection of immutable Unicode characters encased in single, double, or triple quotations.

Python has a variety of built-in string methods that allow programmers to do things like combine, reverse, etc.

Here is a list of Python string functions:


The first character is converted to uppercase.

Syntax: string.capitalize()


Converts string into lower case

Syntax: string.casefold()


The number of times a provided value occurs in a string is returned.

Syntax: string.count(value, start, end)


Returns the position where a supplied value was discovered after searching the string for it.

Syntax: string.find(value, start, end)


Formats a string with provided values.

Syntax: string.format(value1, value2…)


Returns the position where a given value was discovered after searching the string for it.

Syntax: string.index(value, start, end) 


Joins and converts the elements into a string

Syntax: string.join(iterable)


Converts a string to lowercase letters.

Syntax: string.lower()


Replaces a provided value with a specified value and returns a string.

Syntax: string.replace(oldvalue, newvalue, count)


Returns a list after splitting the string at the provided separator.

Syntax: string.split(separator, maxsplit)


Returns a string that has been reduced.

Syntax: string.strip(characters)


Cases are switched, with the lower case becoming the upper case and vice versa.

Syntax: string.swapcase()


Converts a string to upper case letters.

Syntax: string.upper()

Python Dictionary Functions

A Python dictionary is a collection of things with a key and a value for each item. When the key is known, the Dictionaries are optimised to fetch values.

A list of dictionary functions is shown below:


Eliminates all of the dictionary’s elements.

Syntax: dictionary.clear()


Returns a copy of the dictionary

Syntax: dictionary.copy()


Returns a dictionary with the keys and values supplied.

Syntax: dict.fromkeys(keys, value)


  • Keys refers to an iterable specifying the keys of the new dictionary.
  • Value refers to the value for all keys


The value of the given key is returned.

Syntax: dictionary.get(keyname, value)


  • The keyname refers to the keyname of the item you want to return the value from.
  • The value refers to a value to return if the specified key does not exist.


For each key-value pair, returns a list containing a tuple.

Syntax: dictionary.items()


Returns a list containing the dictionary’s keys

Syntax: dictionary.keys()


Removes the element with the specified key

Syntax: dictionary.pop(keyname, defaultvalue)


  • The keyname refers to the item’s keyname that you want to get rid of.
  • The defaultvalue refers to the value to return if the specified key does not exist.


Removes the last inserted key-value pair

Syntax: dictionary.popitem()


Returns the value of the specified key. 

Syntax: dictionary.setdefault(keyname, value)


  • The keyname refers to the item’s keyname from which you wish to retrieve the value.
  • The value specifies the value allocated to the key if it does not already have one.


The dictionary is updated with the provided key-value pairs.

Syntax: dictionary.update(iterable)


  • The iterable refers to an iterable object with key-value pairs that will be inserted into the dictionary.


Returns a list of all the dictionary’s values.

Syntax: dictionary.values()

Python Tuple Functions

A tuple is a set of immutable components. Tuples and lists are similar; however, in the case of tuples, the elements that have been assigned cannot be modified.

The following is a list of functions that can be used to perform tuple functions:


The number of times a given value appears in a tuple is returned.

Syntax: tuple.count(value)


  • The value refers to the value that has been provided.


Returns the position where a specified value was discovered after searching the tuple for it.

Syntax: tuple.index(value)


  • The value refers to the value that has been provided.

Python Set Functions

In Python, a set is a collection of distinct elements that are both ordered and modifiable.

Here is a list of functions that can be used to perform functions on sets:


Adds a new element to the set.

Syntax: set.add(element)


  • The element refers to the element we will be adding to the set.


Removes all the elements from the set

Syntax: set.clear()


This method returns a copy of the set.

Syntax: set.copy()


The difference between two or more sets is returned as a set.

Syntax: set.difference(set)


  • The set refers to the set in which we will be comparing the differences.


Removes items from this set that are also in another set supplied.

Syntax: set.difference_update(set)


  • The set refers to the collection of differences we’ll be comparing.


Remove the specified item.

Syntax: set.discard(value)


  • The value relates to the item that has to be located and removed.


Returns the intersection of two or more sets as a set.

Syntax: set.intersection(set1, set2 … etc)


Removes the items in the current set that are not present in other sets.

Syntax: set.intersection_update(set1, set2 … etc)

is disjoint()

Returns true or false if two sets intersect.

Syntax: set.isdisjoint(set)


  • The set refers to the set to search for similar items.


Returns whether or not this set is part of another set.

Syntax: set.issubset(set)


  • The set refers to the set to search for similar items.


Returns true or false if this set contains another set.

Syntax: set.issuperset(set)


  • The set refers to the set to search for similar items.


Removes one of the set’s elements.

Syntax: set.pop()


Removes the specified element

Syntax: set.remove(item)


  • The item refers to the thing to search for and remove


Return a set with the union of sets in it.

Syntax: set.union(set1, set2…)


Replace the set with a new one or any other iterable.

Syntax: set.update(set)


  • The set refers to the iterable insert into the current set.

Python File Functions

Variables are used to store values in Python. But what if the values are big files rather than words or numbers? Python offers a concept called files because they can’t be saved in variables.

Files store a vast amount of data, and various built-in functions may be used to execute necessary operations on the data stored in the files. They are as follows:


Closes the file

Syntax: file.close()


Returns a number that reflects the stream from the operating system’s standpoint.

Syntax: file.fileno()


Flushes the internal buffer

Syntax: file.flush()


Returns the contents of the file.



Returns whether the file stream is readable.

Syntax: file.readable()


Returns one line from the file

Syntax: file.readline(size)


  • The size refers to the number of bytes from the line to return.


Returns a list of lines from the file

Syntax: file.readlines(hint)


  • The hint refers to the number of bytes returned exceeding the hint number; no more lines will be replaced.


Change the file position.



  • The offset is an integer representing the place in which the current file stream should be set.


Returns the current file position

Syntax: file.tell()


The file is resized to the requested size.

Syntax: file.truncate(size)


If the file can be written to or not, this value is returned.

Syntax: file.writable()


Writes the specified string to the file

Syntax: file.write(byte)


  • The byte refers to the text or byte object that will be inserted.


Writes a list of strings to the file

Syntax: file.writelines(list)


  • The list refers to the list of texts or byte objects that will be inserted.

Essential Python Functions Every Developer Should Know

Though we have mentioned all the necessary functions in a categorical way above, there are still some more that are important and make programming a lot easier. They are:

print( )

prints the specified message to the screen.

Syntax: print(object(s), sep=separator, end=end, file=file, flush=flush)


  • The sep specifies how the objects should be separated.
  • The end specifies what should be printed at the end.
  • The file refers to an object with a write method.
  • The flush specifies whether the output is flushed (True) or buffered (False).

type( ) 

Returns the type of the specified object

Syntax: type(object, bases, dict)

abs( ) 

The absolute value of the provided number is returned.


pow( ) 

Syntax: abs(n)

max( )

returns the item with the highest value

Syntax: max(n1, n2, n3, …)

round( ) 

Delivers a rounded version of the provided value as a floating-point number

Syntax: round(number, digits)

id( ) 

For the supplied object, this function returns a unique id.

Syntax: id(object)

sum( )

The sum of all items is returned.

Syntax: sum(iterable, start)


Functions play an important role in writing an efficient Python program that can run seamlessly without any performance hindrance. 

We hope you’ve gained a better understanding of the importance of functions and how they can be used to improve the program’s quality.

Experience Software Development

Don’t let the information above phase you. If you’ve landed on this page, it’s a good start. If you’re new to software development and want to learn some basic programming, register for our free 5 Day Coding Challenge through the form below. If you’ve already done the coding challenge, we do teach Python as part of our Full Stack Software Development Programme. Click here to find out more. Alternatively, if you want to try some Python, check out our Python cheat sheet.

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