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History to OOPs & Exception Handling — written by CodingNow 2.0's mentors. Free to read, structured to actually help you learn.
Python notes by CodingNow 2.0 cover 194 topics — from python home to mongodb limit — each explained with short definitions, syntax and runnable code examples. They are 100% free, need no signup, and work as quick revision for college exams, Python interviews and CodingNow 2.0's mentor-led Python course in Pitampura, Delhi.
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Python Tutorial
101 of 101 topics publishedPython HOME
Python is a popular programming language.
Python Intro
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
Python Get Started
At W3Schools, you can try Python without installing anything.
Python Syntax
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:
Statements
A computer program is a list of "instructions" to be "executed" by a computer.
Python Output
You have already learned that you can use the print() function to display text or output values:
Print Numbers
You can also use the print() function to display numbers:
Python Comments
Comments can be used to explain Python code.
Python Variables
Variables are containers for storing data values.
Variable Names
A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).
Assign Multiple Values
Python allows you to assign values to multiple variables in one line:
Output Variables
The print() function is often used to output variables.
Global Variables
Variables that are created outside of a function (as in all of the examples in the previous pages) are known as global variables.
Python Data Types
In programming, data type is an important concept.
Python Numbers
Variables of numeric types are created when you assign a value to them:
Python Casting
There may be times when you want to specify a type on to a variable. This can be done with casting. Python is an object-orientated language, and as such it uses
Python Strings
Strings in python are surrounded by either single quotation marks, or double quotation marks.
Slicing Strings
You can return a range of characters by using the slice syntax.
Modify Strings
Python has a set of built-in methods that you can use on strings.
Concatenate Strings
To concatenate, or combine, two strings you can use the + operator.
Format Strings
As we learned in the Python Variables chapter, we cannot combine strings and numbers like this:
Escape Characters
To insert characters that are illegal in a string, use an escape character.
String Methods
Python has a set of built-in methods that you can use on strings.
Python Booleans
Booleans represent one of two values: True or False .
Python Operators
Operators are used to perform operations on variables and values.
Arithmetic Operators
Arithmetic operators are used with numeric values to perform common mathematical operations:
Assignment Operators
Assignment operators are used to assign values to variables:
Ternary Operator
The ternary operator allows you to assign one value if a condition is true, and another if it is false:
Comparison Operators
Comparison operators are used to compare two values:
Logical Operators
Logical operators are used to combine conditional statements:
Identity Operators
Identity operators are used to compare the objects, not if they are equal, but if they are actually the same object, with the same memory location:
Membership Operators
Membership operators are used to test if a sequence is presented in an object:
Bitwise Operators
Bitwise operators are used to compare (binary) numbers:
Operator Precedence
Operator precedence describes the order in which operations are performed.
Python Lists
Lists are used to store multiple items in a single variable.
Access List Items
List items are indexed and you can access them by referring to the index number:
Change List Items
To change the value of a specific item, refer to the index number:
Add List Items
To add an item to the end of the list, use the append() method:
Remove List Items
The remove() method removes the specified item.
Loop Lists
You can loop through the list items by using a for loop:
List Comprehension
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
Sort Lists
List objects have a sort() method that will sort the list alphanumerically, ascending, by default:
Copy Lists
You cannot copy a list simply by typing list2 = list1 , because: list2 will only be a reference to list1 , and changes made in list1 will automatically al
Join Lists
There are several ways to join, or concatenate, two or more lists in Python.
List Methods
Python has a set of built-in methods that you can use on lists.
Python Tuples
Tuples are used to store multiple items in a single variable.
Access Tuples
You can access tuple items by referring to the index number, inside square brackets:
Update Tuples
Tuples are unchangeable, meaning that you cannot change, add, or remove items once the tuple is created.
Unpack Tuples
When we create a tuple, we normally assign values to it. This is called "packing" a tuple:
Loop Tuples
You can loop through the tuple items by using a for loop.
Join Tuples
To join two or more tuples you can use the + operator:
Tuple Methods
Python has two built-in methods that you can use on tuples.
Python Sets
Sets are used to store multiple items in a single variable.
Access Set Items
You cannot access items in a set by referring to an index or a key.
Add Set Items
Note: Once a set is created, you cannot change its items, but you can add new items.
Remove Set Items
To remove an item in a set, use the remove() , or the discard() method.
Loop Sets
You can loop through the set items by using a for loop:
Join Sets
There are several ways to join two or more sets in Python.
Frozenset
frozenset is an immutable version of a set.
Set Methods
Python has a set of built-in methods that you can use on sets.
Python Dictionaries
Dictionaries are used to store data values in key:value pairs.
Access Items
You can access the items of a dictionary by referring to its key name, inside square brackets:
Change Items
You can change the value of a specific item by referring to its key name:
Add Items
Adding an item to the dictionary is done by using a new index key and assigning a value to it:
Remove Items
There are several methods to remove items from a dictionary:
Loop Dictionaries
You can loop through a dictionary by using a for loop.
Copy Dictionaries
You cannot copy a dictionary simply by typing dict2 = dict1 , because: dict2 will only be a reference to dict1 , and changes made in dict1 will automatica
Nested Dictionaries
A dictionary can contain dictionaries, this is called nested dictionaries.
Dictionary Methods
Python has a set of built-in methods that you can use on dictionaries.
Python If...Else
Python supports the usual logical conditions from mathematics:
Python Elif
The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".
Python Else
The else keyword catches anything which isn't caught by the preceding conditions.
Shorthand If
If you have only one statement to execute, you can put it on the same line as the if statement.
Logical Operators
Logical operators are used to combine conditional statements. Python has three logical operators:
Nested If
You can have if statements inside if statements. This is called nested if statements.
Pass Statement
if statements cannot be empty, but if you for some reason have an if statement with no content, put in the pass statement to avoid getting an error.
Python Match
The match statement is used to perform different actions based on different conditions.
Python While Loops
With the while loop we can execute a set of statements as long as a condition is true.
Python For Loops
A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).
Python Functions
A function is a block of code which only runs when it is called.
Python Arguments
Information can be passed into functions as arguments.
Python *args / **kwargs
By default, a function must be called with the correct number of arguments.
Python Scope
A variable is only available from inside the region it is created. This is called scope.
Python Decorators
Decorators let you add extra behavior to a function, without changing the function's code.
Python Lambda
A lambda function is a small anonymous function.
Python Recursion
Recursion is when a function calls itself.
Python Generators
Generators are functions that can pause and resume their execution.
Python Range
The built-in range() function returns an immutable sequence of numbers, commonly used for looping a specific number of times.
Python Arrays
Note: Python does not have built-in support for Arrays, but Python Lists can be used instead.
Python Iterators
An iterator is an object that contains a countable number of values.
Python Modules
Consider a module to be the same as a code library.
Python Dates
A date in Python is not a data type of its own, but we can import a module named datetime to work with dates as date objects.
Python Math
Python has a set of built-in math functions, including an extensive math module, that allows you to perform mathematical tasks on numbers.
Python JSON
JSON is a syntax for storing and exchanging data.
Python RegEx
A RegEx, or Regular Expression, is a sequence of characters that forms a search pattern.
Python PIP
PIP is a package manager for Python packages, or modules if you like.
Python Try...Except
The try block lets you test a block of code for errors.
Python String Formatting
F-String was introduced in Python 3.6, and is now the preferred way of formatting strings.
Python None
None is a special constant in Python that represents the absence of a value.
Python User Input
That means we are able to ask the user for input.
Python VirtualEnv
A virtual environment in Python is an isolated environment on your computer, where you can run and test your Python projects.
Python Classes
10 of 10 topics publishedPython OOP
OOP stands for Object-Oriented Programming.
Python Classes/Objects
Python is an object oriented programming language.
Python __init__ Method
All classes have a built-in method called __init__() , which is always executed when the class is being initiated.
Python self Parameter
The self parameter is a reference to the current instance of the class.
Python Class Properties
Properties are variables that belong to a class. They store data for each object created from the class.
Python Class Methods
Methods are functions that belong to a class. They define the behavior of objects created from the class.
Python Inheritance
Inheritance allows us to define a class that inherits all the methods and properties from another class.
Python Polymorphism
The word "polymorphism" means "many forms", and in programming it refers to methods/functions/operators with the same name that can be executed on many objects
Python Encapsulation
Encapsulation is about protecting data inside a class.
Python Inner Classes
An inner class is a class defined inside another class. The inner class can access the properties and methods of the outer class.
File Handling
4 of 4 topics publishedPython File Handling
File handling is an important part of any web application.
Python Read Files
Assume we have the following file, located in the same folder as Python:
Python Write/Create Files
To write to an existing file, you must add a parameter to the open() function:
Python Delete Files
To delete a file, you must import the OS module, and run its os.remove() function:
Python Matplotlib
13 of 13 topics publishedMatplotlib Intro
! image (https://www.w3schools.com/python/img_matplotlib1.png)
Matplotlib Get Started
If you have Python and PIP already installed on a system, then installation of Matplotlib is very easy.
Matplotlib Pyplot
Most of the Matplotlib utilities lies under the pyplot submodule, and are usually imported under the plt alias:
Matplotlib Plotting
The plot() function is used to draw points (markers) in a diagram.
Matplotlib Markers
You can use the keyword argument marker to emphasize each point with a specified marker:
Matplotlib Line
You can use the keyword argument linestyle , or shorter ls , to change the style of the plotted line:
Matplotlib Labels
With Pyplot, you can use the xlabel() and ylabel() functions to set a label for the x- and y-axis.
Matplotlib Grid
With Pyplot, you can use the grid() function to add grid lines to the plot.
Matplotlib Subplot
With the subplot() function you can draw multiple plots in one figure:
Matplotlib Scatter
With Pyplot, you can use the scatter() function to draw a scatter plot.
Matplotlib Bars
With Pyplot, you can use the bar() function to draw bar graphs:
Matplotlib Histograms
A histogram is a graph showing frequency distributions.
Matplotlib Pie Charts
With Pyplot, you can use the pie() function to draw pie charts:
Machine Learning
23 of 23 topics publishedGetting Started
Machine Learning is making the computer learn from studying data and statistics.
Mean Median Mode
What can we learn from looking at a group of numbers?
Standard Deviation
Standard deviation is a number that describes how spread out the values are.
Percentile
Percentiles are used in statistics to give you a number that describes the value that a given percent of the values are lower than.
Data Distribution
Earlier in this tutorial we have worked with very small amounts of data in our examples, just to understand the different concepts.
Normal Data Distribution
In the previous chapter we learned how to create a completely random array, of a given size, and between two given values.
Scatter Plot
A scatter plot is a diagram where each value in the data set is represented by a dot.
Linear Regression
The term regression is used when you try to find the relationship between variables.
Polynomial Regression
If your data points clearly will not fit a linear regression (a straight line through all data points), it might be ideal for polynomial regression.
Multiple Regression
Multiple regression is like linear regression, but with more than one independent value, meaning that we try to predict a value based on two or more variables.
Scale
When your data has different values, and even different measurement units, it can be difficult to compare them. What is kilograms compared to meters? Or altitud
Train/Test
In Machine Learning we create models to predict the outcome of certain events, like in the previous chapter where we predicted the CO2 emission of a car when we
Decision Tree
! image (https://www.w3schools.com/python/img_ml_decision_tree.png)
Confusion Matrix
It is a table that is used in classification problems to assess where errors in the model were made.
Hierarchical Clustering
Hierarchical clustering is an unsupervised learning method for clustering data points. The algorithm builds clusters by measuring the dissimilarities between da
Logistic Regression
Logistic regression aims to solve classification problems. It does this by predicting categorical outcomes, unlike linear regression that predicts a continuous
Grid Search
The majority of machine learning models contain parameters that can be adjusted to vary how the model learns. For example, the logistic regression model, from
Categorical Data
When your data has categories represented by strings, it will be difficult to use them to train machine learning models which often only accepts numeric data.
K-means
K-means is an unsupervised learning method for clustering data points. The algorithm iteratively divides data points into K clusters by minimizing the variance
Bootstrap Aggregation
Methods such as Decision Trees, can be prone to overfitting on the training set which can lead to wrong predictions on new data.
Cross Validation
When adjusting models we are aiming to increase overall model performance on unseen data. Hyperparameter tuning can lead to much better performance on test sets
AUC - ROC Curve
In classification, there are many different evaluation metrics. The most popular is accuracy, which measures how often the model is correct. This is a great met
K-nearest neighbors
KNN is a simple, supervised machine learning (ML) algorithm that can be used for classification or regression tasks - and is also frequently used in missing val
Python DSA
20 of 20 topics publishedPython DSA
Data Structures is about how data can be stored in different structures.
Lists and Arrays
In Python, lists are the built-in data structure that serves as a dynamic array.
Stacks
A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle.
Queues
A queue is a linear data structure that follows the First-In-First-Out (FIFO) principle.
Linked Lists
A Linked List is, as the word implies, a list where the nodes are linked together. Each node contains data and a pointer. The way they are linked together is th
Hash Tables
A Hash Table is a data structure designed to be fast to work with.
Trees
A tree is a hierarchical data structure consisting of nodes connected by edges.
Binary Trees
A tree is a hierarchical data structure consisting of nodes connected by edges.
Binary Search Trees
A Binary Search Tree is a Binary Tree where every node's left child has a lower value, and every node's right child has a higher value.
AVL Trees
The AVL Tree is a type of Binary Search Tree named after two Soviet inventors Georgy Adelson-Velsky and Evgenii Landis who invented the AVL Tree in 1962.
Graphs
A Graph is a non-linear data structure that consists of vertices (nodes) and edges.
Linear Search
Linear search (or sequential search) is the simplest search algorithm. It checks each element one by one.
Binary Search
The Binary Search algorithm searches through a sorted array and returns the index of the value it searches for.
Bubble Sort
Bubble Sort is an algorithm that sorts an array from the lowest value to the highest value.
Selection Sort
The Selection Sort algorithm finds the lowest value in an array and moves it to the front of the array.
Insertion Sort
The Insertion Sort algorithm uses one part of the array to hold the sorted values, and the other part of the array to hold values that are not sorted yet.
Quick Sort
As the name suggests, Quicksort is one of the fastest sorting algorithms.
Counting Sort
The Counting Sort algorithm sorts an array by counting the number of times each value occurs.
Radix Sort
The Radix Sort algorithm sorts an array by individual digits, starting with the least significant digit (the rightmost one).
Merge Sort
The Merge Sort algorithm is a divide-and-conquer algorithm that sorts an array by first breaking it down into smaller arrays, and then building the array back t
Python MySQL
12 of 12 topics publishedMySQL Get Started
Python can be used in database applications.
MySQL Create Database
To create a database in MySQL, use the "CREATE DATABASE" statement:
MySQL Create Table
To create a table in MySQL, use the "CREATE TABLE" statement.
MySQL Insert
To fill a table in MySQL, use the "INSERT INTO" statement.
MySQL Select
To select from a table in MySQL, use the "SELECT" statement:
MySQL Where
When selecting records from a table, you can filter the selection by using the "WHERE" statement:
MySQL Order By
Use the ORDER BY statement to sort the result in ascending or descending order.
MySQL Delete
You can delete records from an existing table by using the "DELETE FROM" statement:
MySQL Drop Table
You can delete an existing table by using the "DROP TABLE" statement:
MySQL Update
You can update existing records in a table by using the "UPDATE" statement:
MySQL Limit
You can limit the number of records returned from the query, by using the "LIMIT" statement:
MySQL Join
You can combine rows from two or more tables, based on a related column between them, by using a JOIN statement.
Python MongoDB
11 of 11 topics publishedMongoDB Get Started
Python can be used in database applications.
MongoDB Create DB
To create a database in MongoDB, start by creating a MongoClient object, then specify a connection URL with the correct ip address and the name of the database
MongoDB Collection
Note: A collection in MongoDB is the same as a table in SQL databases.
MongoDB Insert
Note: A document in MongoDB is the same as a record in SQL databases.
MongoDB Find
Note: In MongoDB we use the find() and find_one() methods to find data in a collection. Just like the SELECT statement is used to find data in a table
MongoDB Query
When finding documents in a collection, you can filter the result by using a query object.
MongoDB Sort
Use the sort() method to sort the result in ascending or descending order.
MongoDB Delete
To delete one document, we use the delete_one() method.
MongoDB Drop Collection
You can delete a table, or collection as it is called in MongoDB, by using the drop() method.
MongoDB Update
You can update a record, or document as it is called in MongoDB, by using the update_one() method.
MongoDB Limit
To limit the result in MongoDB, we use the limit() method.
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