#!/usr/bin/env python
# coding: utf-8

# ---   
#  <img align="left" width="75" height="75"  src="https://upload.wikimedia.org/wikipedia/en/c/c8/University_of_the_Punjab_logo.png"> 
# 
# <h1 align="center">Department of Data Science</h1>
# <h1 align="center">Course: Tools and Techniques for Data Science</h1>
# 
# ---
# <h3><div align="right">Instructor: Muhammad Arif Butt, Ph.D.</div></h3>    

# <h1 align="center">Lecture 2.3</h1>

# <a href="https://colab.research.google.com/github/arifpucit/data-science/blob/master/Section-2-Basics-of-Python-Programming/Lec-2.03-Variables-Number-Operators/01-variables.ipynb" target="_parent"><img src="https://colab.research.google.com/assets/colab-badge.svg" alt="Open In Colab"/></a>

# ## _01-variables.ipynb_
# #### [Python Built-in Types](https://docs.python.org/3/library/stdtypes.html#)

# ## Learning agenda of this notebook
# Variables are used to store data in computer memory
# 1. Python is dynamically typed
# 2. Intellisense / Code Completion
# 3. Variables and variable naming conventions
# 4. Assigning values to multiple variables in single line
# 5. Checking type of a variable using Built-in `type()` function
# 6. Checking ID of a variable using Built-in `id()` function
# 7. Do we actually store data inside variables?
# 8. Deleting a variable from Kernel memory

# ## 1. You don't have to specify a data type in Python, since it is a dynamically typed language

# > **Variables**: While working with a programming language such as Python, information is stored in *variables*. You can think of variables as containers for storing data. The data stored within a variable is called its *value*.

# In[1]:


name_of_instructor = "Arif Butt"
name_of_instructor
type(name_of_instructor)


# In[4]:


no_of_lectures = [32.5, 66]
no_of_lectures
typeq


# ## 2.  Intellisense/Code Completion
# - Intellisense or Code completion is a general term for various code editing features including: code completion, parameter info, quick info, and member lists. 
#     * **Autocompletion:** Type few characters of a variable or function name and then press tab to get a list, press enter to complete. While typing the name of an existing variable in a code cell within Jupyter, just type the first few characters and press the `Tab` key to autocomplete the variable's name. Try typing `nam` in a code cell below and press `Tab` to autocomplete to `name_of_instructor`.
#     * **Intellisense:** After the name of a object, put a `Dot`, then press `Tab` to get a list of all the attributes and methods of that object
#     * **Tooltip:** With the cursor on the name of the method, press <shift+tab> to get a tool tip, that describes what the method does, and what parameters it takes

# ## 3. Variable Naming Conventions
# - In programming languages, **identifiers** are names used to identify a variable, function, or other entities in a program. Variable names can be short (`a`, `x`, `y`, etc.) or descriptive ( `my_favorite_color`, `profit_margin`, `the_3_musketeers`, etc.). However, you must follow these rules while naming Python variables:
#     - An identifier or variable's name must start with a letter or the underscore character `_`. It cannot begin with a number.
#     - A variable name can only contain lowercase (small) or uppercase (capital) letters, digits, or underscores (`a`-`z`, `A`-`Z`, `0`-`9`, and `_`).
#     - Spaces are not allowed. Instead, we must use snake_case to make variable names readable.
#     - Variable names are case-sensitive, i.e., `a_variable`, `A_Variable`, and `A_VARIABLE` are all different variables.
# 
# - Keywords are reserved words. Each keyword has a specific meaning to the Python interpreter. A reserved keyword may not be used as an identifier. Here is a list of the Python keywords.
# ```
# False               class               from                or
# None                continue            global              pass
# True                def                 if                  raise
# and                 del                 import              return
# as                  elif                in                  try
# assert              else                is                  while
# async               except              lambda              with
# await               finally             nonlocal            yield
# break               for                 not                 
# ```
# 
# - To get help about these keywords: Type `help('keyword')` in the cell below

# In[5]:


help('True')


# In[ ]:


# True is a keyword, can't be used as variable name
#True = 100


# In[ ]:


# A variable name cannot start with a special character or digit
var1 = 25
#1var = 530
#@i = 980


# <h1 align="center">Python Datatypes</h1>
# 
# <img align="center" width="800" height="800"  src="images/datatypes.png" > 
# 
# 
# 

# - Python's Number data types are created by numeric literals and returned as results by arithmetic operators and arithmetic built-in functions. ALL Numeric objects are immutable; once created their value never changes.
#     - Integer
#     - Floating Point
#     - Complex
#     - Bolean
#     - **Boolean:** Also 
# - A Python sequence is an ordered collection of items, where each item is indexed by an integer value. There are three types of sequence types in Python:
#     - String
#     - List
#     - Tuple
# - In Python, a Set is an unordered collection of data type that is iterable, mutable and has no duplicate elements. The order of elements in a set is undefined.
#     - Set (mutable)
#     - Frozenset (immutable)
# - Mapping is an unordered data type in Python. Currently, there is only one standard mapping data type in Python called Dictionary.

# In[ ]:


a = range(10)


# In[ ]:


type(a)


# ## 4. Assign Multiple values to Multiple variables in one Statement

# In[ ]:


#Assigning multiple values to multiple variables
a, b, c = 5, 3.2, "Hello"

print ('a = ',a,' b = ',b,' c = ',c)


# ## 5. To Check the Type of a Variable

# In[6]:


# to check the type of variable
name = "Arif Butt"
print("name is of ", type(name))
x = 234
print("x is of ", type(x))
y = 5.321
print("y is of ", type(y))


# ## 6. To Check the ID of a Variable
# - Every Pyton object has an associated ID (memory address). The Python built-in `id()` function returns the identity of an object

# In[7]:


x = 234
y = 5.321
id(x), id(y)


# ## 7. Do we actually store data inside variables

# In[8]:


a = 10
b = 10
id(a), id(b)


# >- Both the variables `a` and `b` have same ID, i.e., both a and b are pointing to same memory location.
# >- Variables in Python are not actual objects, rather are references to objects that are present in memory. 
# >- So both the variables a and b are refering to same object 10 in memory and thus having the same ID.

# In[9]:


var1 = "Data Science"
id(var1)


# In[10]:


var1 = "Arif Butt"
id(var1)


# >Note that the string object "Data Science" has become an orphaned object, as no variable is refering to it now. This is because the reference `var1` is now pointing/referring to a new object "Arif Butt". All orphan objects are reaped by Python garbage collector.

# ## 8. Use of `dir()`, and `del` Keyword
# - The built-in `dir()` function, when called without an argument, return the names in the current scope.
# - If passed a 
#     - object name: 
#     - module name: then returns the module's attributes
#     - class name: then returns its attributes and recursively the attributes of its base classes
#     - object name: then returns its attributes, its class's attributes, and recursively the attributes of its class's base classes.

# In[11]:


print(dir())


# In[12]:


newvar = 10
print("newvar=", newvar)


# In[13]:


print(dir())


# In[14]:


del var1
print(dir())


# In[15]:


var1


# In[16]:


import math
print(dir(math))


# In[ ]:





# ## Check your Concepts
# 
# Try answering the following questions to test your understanding of the topics covered in this notebook:
# 
# 1. What is a variable in Python?
# 2. How do you create a variable?
# 3. How do you check the value within a variable?
# 4. How do you create multiple variables in a single statement?
# 5. How do you create multiple variables with the same value?
# 6. How do you change the value of a variable?
# 7. How do you reassign a variable by modifying the previous value?
# 8. What are the rules for naming a variable?
# 9. Are variable names case-sensitive? Do `a_variable`, `A_Variable`, and `A_VARIABLE` represent the same variable or different ones?
# 10. How do you check the data type of a variable?