#Python-Basic  #Python 

2.1 Data Types

Data Type represent the type of data present inside a variable. In Python, we are not required to specify the type explicitly.

Based on value provided, the type will be assigned automatically. Hence, Python is Dynamically Typed Language.

Python contains the following inbuilt data types

Char Type:        str
Numeric Types:    int, float, complex
Sequence Types:   list, tuple, range
Mapping Type:     dict
Set Types:        set,  frozenset
Boolean Type:     bool
Binary Types:     bytes, bytearray, memoryview
None Type:        NoneType

2.2 Python contains several inbuilt functions

  • type()
    • to check the type of variable
  • id()
    • to get address of object
  • print()
    • to print the value

In Python everything is an object.

2.3 Dynamic type and Strong Type

Dynamic Type

  • Python is dynamic typing language
  • We don’t specify types in advance, the object types is resolved at runtime
  • Dynamic typing allows for flexibility in programming, but with a price in performance .

Duck Type

  • Also called as Duck typing language
  • Duck typing means that we are not interested in what type an object is
  • Instead, we are more concerned in the functional aspect of the object

If a bird that walks like a duck and swims like a duck and quacks like a duck, that bird is a duck

Strong Type

  • Python uses strong typing, type-coercion is not allowed.
  • Every object has a specific type
  • There is no implicit type conversion
  • 9 + ‘9’ –> Error in python

2.5 int data type

We can use int data type to represent whole numbers (integral values)

In Python2 we have long data type to represent very large integral values. But in Python3 there is no long type explicitly, and we can represent long values also by using int type only.

2.5.1 Represent different Number System

1. Decimal form(base-10)

  • It is the default number system in Python
  • The allowed digits are: 0 to 9
a = 10

2. Binary form(Base-2)

  • The allowed digits are : 0 & 1
  • Literal value should be prefixed with 0b or 0B
a = 0B1111
a = 0B123
a = 0b111

3. Octal Form(Base-8)

  • The allowed digits are : 0 to 7
  • Literal value should be prefixed with 0o or 0O
a = 0o123
a = 0o786

4. Hexa Decimal Form(Base-16)

  • The allowed digits are : 0 to 9, a-f (both lower and upper cases are allowed)
  • Literal value should be prefixed with 0x or 0X
a = 0XFACE
a = 0XBeer

Note:

  • Being a programmer we can specify literal values in decimal, binary, octal and hexadecimal forms.
  • But PVM will always provide values only in decimal form.
print(10)   # 10
print(0o10) # 8
print(0X10) # 16
print(0B10) # 2

2.5.2 Base Conversions

Python provide the following in-built functions for base conversions

  1. bin()
  • We can use bin() to convert from any base to binary
bin(15)  # '0b1111'
bin(0o11)  #'0b1001'
bin(0X10) # '0b10000'
  1. oct()
  • We can use oct() to convert from any base to octal
oct(10)  # '0o12'
oct(0B1111)  # '0o17'
oct(0X123)  # '0o443'
  1. hex()
  • We can use hex() to convert from any base to hexadecimal
hex(100)  # '0x64'
hex(0B111111)  # '0x3f'
hex(0o12345)  # '0x14e5'

2.6 float data type

We can use float data type to represent floating point values (decimal values)

We can also represent floating point values by using exponential form (scientific notation)

We can represent float values only by using decimal form.

print(1.234)
print(1.2e3) # 1200.0

print(0B11.01)  # SyntaxError: invalid syntax

2.7 Complex Data Type

A complex number is of the form a + bj, a and b contain integers or floating point values

  • In the real part(a) –> can use decimal, octal,binary or hexadecimal form.
  • But imaginary part(bj) –> can use only decimal form.

Note

  • Complex data type has some inbuilt attributes to retrieve the real part and imaginary part
c = 10.5+3.6j
c.real  # 10.5
c.imag  # 3.6

2.8 bool data type

  • We can use this data type to represent boolean values
  • The only allowed values for this data type are - True and False
  • Internally Python represents True as 1 and False as 0
bool(0)  # False
# All other no is True

bool('')  # False
# All other string is True


True + True  # 2
True + False # 1
True - True  # 0

2.9 str type

A String is a sequence of characters enclosed within single quotes or double quotes or triple quotes.

a1 = 'Amrit'

a2 = '''Amrit
        Prasad'''

a3 = '''This "Python class very helpful" for java students'''

Slicing of Strings

  • Slice means a piece
  • [ ] operator is called slice operator, which can be used to retrieve parts of String.
a1 = 'Amrit'

-5 -4 -3 -2 -1
 A  m  r  i  t
 0  1  2  3  4

a1[2:]  # rit
a1[:2]  # Am

a1[::2]  # 'Art'

#  a1[::-1]  # 'tirmA'

2.10 bytes Data type

Bytes data type represents a group of byte numbers just like an array.

The only allowed values for byte data type are 0 to 256. By mistake if we are trying to provide any other values then we will get value error.

Once we create bytes data type value, we cannot change its values,otherwise we will get TypeError.

x = [10,20,30,40]
b = bytes(x)

type(b)  # bytes
print(b[0])   # 10
print(b[-1])  # 40

# TypeError: 'bytes' object does not support item assignment
b[0]=100

# ValueError: byte must be in range(0, 256)
bytes([277])

2.11 bytearray Data type

Bytearray is exactly same as bytes data type except that its elements can be modified

x = [10,20,30,40]
b = bytearray(x)

type(b)  # bytes
print(b[0])   # 10
print(b[-1])  # 40

# No Error
b[0]=100

# ValueError: byte must be in range(0, 256)
bytearray([277])

2.12 frozenset Data type

It is exactly same as set except that it is immutable. Hence, we cannot use add or remove functions.

s={10,20,30,40}
type(s)  # set

fs = frozenset(s)
type(fs)  # frozenset

2.13 range Data Type

  • range Data Type represents a sequence of numbers.
  • The elements present in range Data type are not modifiable. i.e range Data type is immutable.
range(10) # range(0, 10)
generate numbers from 0 to 9

range(10,20)
# generate numbers from 10 to 19

r = range(10,20,2)
# 2 means increment value
for i in r : print(i)   # 10,12,14,16,18

2.14 Python collections

  • Python has 4 built-in data structures that can be used to hold a collection of objects,
  • They are list, tuple, set, and dictionary

2.14.1 list

# Def empty list
p = list()
p = []

nlist = [10, 10.5, 'ap', True, 20]

2.14.2 Dictionary

# Def empty dict
p = dict()
p = {}

dict([(1,2), (3,4)])
# {1: 2, 3: 4}

{'a': 1, 3: 'aa'}

2.14.3 set

# Def empty set
p = set()
# p = {}   # `Not set but dict`

{1,2,'a'}

# Fxn
* add()
* update()
* remove()

# Element contains in set must be `immutable type only`
# Coz immutable are hashable
p.add([1,2])  # --> Error
p.add((1,2))  # --> Ok

2.14.4 tuple

# Def empty tuple
p = ()
p = tuple() 

p = 1,2,3,4     
# (1, 2, 3, 4)

# Convert into tuples
tuple([1,2,3])
# (1,2,3)

tuple("Amrit")
# ('A', 'm', 'r', 'i', 't')

2.15 Data Types Differences

# Mutable objects
list, set
bytearray

dict 
# Dict maps immutable keys to mutable values
# Dict - keys should be immutable, Coz immutable are hashable

# Immutable objects
tuple
int, float, complex, bool, str
bytes, frozenset, range

# Unordered
dict, set

# Homogeneous
* str

2.16 Hashable

  • Immutable types are hashable
  • But mutable types (lists, dictionaries, set) are not.

2.17 Difference Between List and Array in Python

  • Element data types
    • List: Any type
    • Array: Same type
  • Declaration
    • List: Not required
    • Array: Declaration is required
  • Arithmetic operations
    • List: Cannot directly handle
    • Array: Can directly handle
  • Nested
    • List: Nested lists can be of variable size
    • Array: Nested arrays has to be of same size.