PYTHON PROGRAMMING FOR ABSOLUTE BEGINNER
What is Python?
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
It is used for:
- web development (server-side),
- software development,
- mathematics,
- system scripting.
What can Python do?
- Python can be used on a server to create web applications.
- Python can be used alongside software to create workflows.
- Python can connect to database systems. It can also read and modify files.
- Python can be used to handle big data and perform complex mathematics.
- Python can be used for rapid prototyping, or for production-ready software development.
Why Python?
- Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
- Python has a simple syntax similar to the English language.
- Python has syntax that allows developers to write programs with fewer lines than some other programming languages.
- Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick.
- Python can be treated in a procedural way, an object-orientated way or a functional way.
Good to know
- The most recent major version of Python is Python 3, which we shall be using in this tutorial. However, Python 2, although not being updated with anything other than security updates, is still quite popular.
- In this tutorial Python will be written in a text editor. It is possible to write Python in an Integrated Development Environment, such as Thonny, Pycharm, Netbeans or Eclipse which are particularly useful when managing larger collections of Python files.
Python Syntax compared to other programming languages
- Python was designed for readability, and has some similarities to the English language with influence from mathematics.
- Python uses new lines to complete a command, as opposed to other programming languages which often use semicolons or parentheses.
- Python relies on indentation, using whitespace, to define scope; such as the scope of loops, functions and classes. Other programming languages often use curly-brackets for this purpose.
Execute Python Syntax
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:
>>> print("Hello, World!")
Hello, World!
Python Indentation
Indentation refers to the spaces at the beginning of a code line.
Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important.
Python uses indentation to indicate a block of code.
Example
print("Five is greater than two!")
Python Variables
In Python, variables are created when you assign a value to it:
Comments
Python has commenting capability for the purpose of in-code documentation.
Comments start with a #, and Python will render the rest of the line as a comment:
#This is a comment.
print("Hello, World!")
Built-in Data Types
In programming, data type is an important concept.
Variables can store data of different types, and different types can do different things.
Python has the following data types built-in by default, in these categories:
Specify a Variable Type
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 classes to define data types, including its primitive types.
Python Casting
Casting in python is therefore done using constructor functions:
- int() - constructs an integer number from an integer literal, a float literal (by rounding down to the previous whole number), or a string literal (providing the string represents a whole number)
- float() - constructs a float number from an integer literal, a float literal or a string literal (providing the string represents a float or an integer)
- str() - constructs a string from a wide variety of data types, including strings, integer literals and float literals.
String Literals
String literals in python are surrounded by either single quotation marks, or double quotation marks.
'hello'is the same as "hello".
You can display a string literal with the print() function:
Python Booleans
Boolean Values
In programming you often need to know if an expression is true or false.
You can evaluate any expression in Python, and get one of two answers, true or false.
When you compare two values, the expression is evaluated and Python returns the Boolean answer:
When you run a condition in an if statement, Python returns true or false. :
Example
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")
Python Operators
Python Operators
Operators are used to perform operations on variables and values.
Python divides the operators in the following groups:
- Arithmetic operators
- Assignment operators
- Comparison operators
- Logical operators
- Identity operators
- Membership operators
- Bitwise operators
| Operator | Example | Same As | |
|---|---|---|---|
| = | x = 5 | x = 5 | |
| += | x += 3 | x = x + 3 | |
| -= | x -= 3 | x = x - 3 | |
| *= | x *= 3 | x = x * 3 | |
| /= | x /= 3 | x = x / 3 | |
| %= | x %= 3 | x = x % 3 | |
| //= | x //= 3 | x = x // 3 | |
| **= | x **= 3 | x = x ** 3 | |
| &= | x &= 3 | x = x & 3 | |
| |= | x |= 3 | x = x | 3 | |
| ^= | x ^= 3 | x = x ^ 3 | |
| >>= | x >>= 3 | x = x >> 3 | |
| <<= | x <<= 3 | x = x << 3 |
Python Comparison OperatorsComparison operators are used to compare two values:
|
Python Logical Operators
Logical operators are used to combine conditional statements:
| Operator | Description | Example | Try it |
|---|---|---|---|
| and | Returns True if both statements are true | x < 5 and x < 10 | |
| or | Returns True if one of the statements is true | x < 5 or x < 4 | |
| not | Reverse the result, returns False if the result is true | not(x < 5 and x < 10) |
Python Membership Operators
Membership operators are used to test if a sequence is presented in an object:
| Operator | Description | Example | |
|---|---|---|---|
| in | Returns True if a sequence with the specified value is present in the object | x in y | |
| not in | Returns True if a sequence with the specified value is not present in the object | x not in y |
Python Bitwise Operators
Bitwise operators are used to compare (binary) numbers:
| Operator | Name | Description |
|---|---|---|
| & | AND | Sets each bit to 1 if both bits are 1 |
| | | OR | Sets each bit to 1 if one of two bits is 1 |
| ^ | XOR | Sets each bit to 1 if only one of two bits is 1 |
| ~ | NOT | Inverts all the bits |
| << | Zero fill left shift | Shift left by pushing zeros in from the right and let the leftmost bits fall off |
| >> | Signed right shift | Shift right by pushing copies of the leftmost bit in from the left, and let the rightmost bits fall off |
Python Collections (Arrays)
There are four collection data types in the Python programming language:
- List is a collection which is ordered and changeable. Allows duplicate members.
- Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
- Set is a collection which is unordered and unindexed. No duplicate members.
- Dictionary is a collection which is unordered, changeable and indexed. No duplicate members.
When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.
List
A list is a collection which is ordered and changeable. In Python lists are written with square brackets.
Example
print(thislist)
Tuple
A tuple is a collection which is ordered and unchangeable. In Python tuples are written with round brackets.
Example
print(thistuple[1])
Set
A set is a collection which is unordered and unindexed. In Python sets are written with curly brackets.
Example
print(thisset)