4)Python Variables and Data Types

Python Variables and Data Types:

Python Variables:
A variable is a location in memory used to store data(value).

Note:

• We don't need to declare a variable before using it. In Python, we simply assign a value to a variable and it will exist. 
• Also don't even have to declare the type of the variable. This is handled internally according to the type of value we assign to the variable.

Single Variable assignment
Example:

x=10

Multiple assignments

• Multiple assignments with different values

x,y,z=10,'A',10.20

• Multiple assignments with same values

x=y=z=10

Python Data types:

Every value in Python has a datatype. Since everything is an object in Python programming, data types are classes and variables are instance (object) of these classes.

Let's go through with some important data types:

1)Python Numbers

Integers, floating point and complex numbers falls under Python numbers category

In Python repository, there are int, float and complex classes

Note:

• type() function to know which class a variable or a value belongs to
• isinstance() function to check if an object belongs to a particular class.

Example:

Note:

Floating numbers can hold up to 15 decimal places, if exceeds, other parts will be truncated

2)Python List:

List is an ordered sequence of items.

Note:

All the items in a list do not need to be of the same type.

Declaration:

Separated by commas are enclosed within brackets [ ].

Slicing operator [ ]:

To extract an item or a range of items from a list. Index starts form 0 in Python.

3)Python Tuple:
Tuple is an ordered sequence of items same like list.

Note:

• The only difference is that tuples are immutable. Tuples once created cannot be modified, it returns an exception
• Tuples are used to write and protect data, are usually faster than list as it cannot change dynamically.

Declaration:
Separated by commas within parenthesis or braces,

Slicing operator [ ]:
For tuples, using slicing operator, only retrieving the values can be allowed, but not allow the value change


Example:

4)Python Strings:
String is sequence of Unicode characters.

Declaration:

• single line strings are with single quotes or double quotes 
• Multi-line strings can be denoted using triple quotes, ''' or """.

Slicing operator [ ]:
For String, using slicing operator, only retriving the values can be allowed, but not allow the value change

Example:

5)Python Set:
Set is an unordered collection of unique items.

Declaration:
Set is defined by values separated by comma inside curly braces { }. 

Note:

• Items in a set are not ordered and not indexed so slicing operator wont work with sets
• We can perform set operations like union, intersection on two sets. Set have unique values. They eliminate duplicates.

Example:

6)Python Dictionary:

Dictionary is an unordered collection of key-value pairs.

Declaration:
In Python, dictionaries are defined within braces {} with each item being a pair in the form key:value. Key and value can be of any type.

Note:
To retrieve value of dictionary can be done through only the key

Conversion between data types:

Below functions are useful to convert datatypes ,

int(), float(), str(),set(),tuple(),list() ,dict() etc.

Example:

>>> float(5)
5.0
>>> int(10.6)
10
>>> str(25)
'25'
>>> set([1,2,3])
{1, 2, 3}
>>> tuple({5,6,7})
(5, 6, 7)
>>> list('hello')
['h', 'e', 'l', 'l', 'o']
>>> dict([[1,2],[3,4]])
{1: 2, 3: 4}
>>> dict([(3,26),(4,44)])
{3: 26, 4: 44}

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