variableT.py

# CREATING VARIABLE
x = 10.583753
name = "Python"
a = b = c = 5             # multiple assignment
p, q = 1, 2              # unpacking during assignment

#input
x = float(input("Enter a number: "))
name = input("Enter your name: ")

# printing and formatting
print("Id is",end=" ")  # end parameter to avoid newline
print(id(name)) # memory address of the variable
print(type(x))           # <class 'int'>
print(type(name))        # <class 'str'>
print(name)
print("Value:", x)
print(name, x, sep=" | ")  # Name: Python | Value: 10.583753
print(f"Name: {name}, Value: {x}")  # f-string formatting
print("Name: {}, Value: {}".format(name, x))  # str.format() method
print(f"Value: {x:3.2f}")  # 2 decimal places and 3 digit place reserved before decimal
print("Age: {1} Name: {0}".format(name, x)) # with index
print("Name: {n} Age: {a}".format(n=name, a=x)) # with keyword
# alignment
print(f"{name:>10}")   # right align
print(f"{name:<10}")   # left align
print(f"{name:^10}")   # center align

# DATA TYPES
# numeric
i = 10                   # int
f = 3.14                 # float
c = 2 + 3j               # complex
# string
s = "hello"
# sequence
lst = [1, 2, 3]          # list
tup = (1, 2, 3)          # tuple
rng = range(5)           # range
# binary
b = bytes([65, 66])      # byte
ba = bytearray([65, 66]) # bytearray
mv = memoryview(b)       # memoryview
# dictionary
dct = {"a": 1, "b": 2}
# set
st = {1, 2, 3}
fs = frozenset([1, 2, 3])
# boolean
flag = True # boolean value can be True or False
#0 and 1 can also be used as boolean values where 0 is False and 1 is True
flag=bool(0) # False
flag=bool(1) # True
flag=bool(None) # False
flag=bool("") # False
flag=bool("False") # True (non-empty string is True)
flag=bool([]) # False
flag=bool([0]) # True (non-empty list is True)
flag=bool({}) # False
flag=bool({0: "zero"}) # True (non-empty dict is True)
flag=bool(set()) # False
flag=bool({0}) # True (non-empty set is True)
flag=bool(0.0) # False
flag=bool(0.1) # True (non-zero float is True)
if(1):print("This will always execute as 1 is treated as True")
if(not None): print("This will execute as None is treated as False")
# none
n = None

#type of variable:global, local, nonlocal
global_var1 = "global"
global_var2 = "global"
def outer():
    outer1 = "local"
    outer2 = "local"
    global_var2 = "local" #creating new variable, not representing global variable
    global global_var1 #represent global variable, not creating new variable
    global_var1 = "modified global"
    
    def inner():
        nonlocal outer1 #represent immediate outer variable, it is not creating new variable
        outer1 = "nonlocal"
        
        outer2 = "local" #creating new variable, not representing outer variable
        
        global global_var1 #represent global variable, not creating new variable
        global_var1 = "modified global from inner"
        
        print("inner:", outer1)
        print("inner:", outer2)
        print("inner:", global_var1)
    inner()
    print("outer:", outer1)
    print("outer:", global_var1)
outer()

# TYPE CASTING
# implicit
x = 10
y = 2.5
z = x + y                # int -> float automatically
print(z)
# explicit
print(int("10"))         # string to int
print(float(5))          # int to float
print(complex(2, 3))     # complex
print(str(100))          # to string
print(tuple([1, 2]))     # list -> tuple
print(list((1, 2)))      # tuple -> list
print(set([1, 2, 2]))    # remove duplicates
print(dict([(1, 'a'), (2, 'b')])) # list of tuples to dict
print(chr(65))           # A
print(ord('A'))          # 65
print(hex(255))          # 0xff
print(oct(8))            # 0o10

# eval (use carefully)
print(eval("2 + 3"))     # 5


# PACKING AND UNPACKING
# packing
t = 1, 2, 3              # tuple packing
# unpacking
a, b, c = t
print(a, b, c)
# extended unpacking (* for remaining elements)
t = (10, 20, 30, 40, 50, 60)
x, *y, z = t
print(x)  # first value
print(y)  # middle values
print(z)  # last value

# DELETING VARIABLE
temp = 100
del temp
# print(temp)            # ERROR: variable deleted