1. Introduction
Python is an interpreted, object-oriented and high-level programming language, which is different from a compiled one like C/C++/Java.
Its code is concise but at the same highly readable (pythonic).
It is dynamically typed: a variables does not need a predefined type.
Other than the basic types, It also has built-in collection types:
lists
tuples
dictionaries (maps)
sets
It can be linked to C/C++/Java codes that handle time-critical jobs more efficiently.
It has a large collection of standard and special-purpose libraries.

2. Other Features
It uses indentations (not braces or keywords) to define blocks.
It has three frequently used sequence types:
strings: ‘xyz’, immutable, for characters.
lists: […], mutable, for any objects.
tuples: (…), immutable, for any objects.
It supports multiple paradigms (obj-oriented, functional, procedural).
It has powerful subscripting/slicing methods.
It is one of the most popular scripting languages (Perl, PHP, Tcl, JavaScript and Unix shell scripts).
It has found numerous applications, especially in string/text manipulation, file/directory management, and web design.
It is open-source and is available in all major systems.

3. Comparison C/C++/Java Statically typed.
A variable’s type must be declared before it can be used.
Methods use type signatures to enforce contracts.
Python
Dynamically typed.
A variables comes into existence when first assigned a value.
A variable can refer to an object of any type.
Most types are treated the same way.
Drawback: type errors are caught at runtime only.

4. Python Versions Python 2.x The latest stable release: 2.7
It implements certain new features of 3.x and is fully backwards compatible.
Python 3.x
The latest release: 3.6.2
Strings use Unicode, not ASCII.
It contains many new features and are cleaner.
It has compatibility issues with the legacy codes written with 2.x versions.

5. Run Python interactively (command-line mode)
Python 2.5 (r25:51908, May , 16:14:04)
[GCC (prerelease) (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> 2+3 5
“>>>” is the Python prompt sign.
“CTRL-D” to exit Python.

6. Run Python code in a file
% python example.py
--- Add this line at the top of the file: #!/usr/bin/python
--- Make the file executable.
We will run Python in the IDLE environment (to be discussed in lab sessions).

7. A Code Sample
# This is a Python code sample. a = 22 b = a + 33 c = d = "YSU" if a == 44 or d == "YSU": a = a +1 d = d + "Football" print (a) print (b) print (c) print (d)

8. Explanations
Indentation has special meanings: It indicates a block structure.
The first assignment to a variable creates it.
A variable’s type does not need to be declared.
Python figures out a variable type in the context.
“=“ is assignment operator, and “==“ is comparison operator.
“+”, “-”, “*”, “/”, “%” are arithmetic operators.
“+” means concatenation for strings.
“%” indicates formatting for a string (similar to “printf” in C).
Logical operators are words (and, or, not).
Simple I/O:
num = input ('Enter a number: ')
print (*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

9. Basic Types Integers (default for numbers) x = 34 Floating points
Strings
s1 = “YSU”
s2 = ‘YSU’

10. Whitespace and Indentation
Whitespace has special meanings in Python.
Within an expression or a statement, whitespaces are ignored.
Leading whitespace of a line defines indentation.
Consistent indentations define blocks.
The first line with less indentation is outside of the block.
The first line with more indentation starts a nested block.
A colon often appears at the start of a new block (function and class).
A newline ends a line of code.
Continuation of a long line to the next line is indicated by putting the backslash character (\) at the end of a line.

11. Assignments
In Python, binding a variable means setting a name to hold a reference to an object. Assignment creates references, not copies (as in Java)
A variable is created the first time it appears on the left side of an assignment expression:
An object is deleted (by garbage collector) once it becomes unreachable.
Names in Python do not have an intrinsic type.
Objects have types. Python determines the type of a reference automatically based on what data is assigned to it.