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Variables

In Python, we store all pieces of data -- numbers, characters, strings, everything -- as objects, and we refer to these objects using variables. As a simple case, we can assign a variable a value using the assignment operator, which is the "equals" sign. Python's order of operations is the same as that of normal mathematics: parentheses first, then exponentiation, then multiplication/division, and then addition/subtraction.

x = 4
y = 5
z = x + y
print(z)
stri="Hello" # or stri='Hello' No difference in python between "" and ''
print(stri + str(z))
a=True
print(a)
b=(1==3)
print(b)

9
Hello9
True
False

Three tools for understanding strange objects

type() function

  • type() (what is this thing?) To inspect which type is a variable use type().

dir() function

  • dir() (what can I do with it?)

help() function

  • help() (tell me more) 
    print(type(z))
print(type(a))
print(type(stri))
print(dir(2))
#print(help(2))

    <class 'int'>
<class 'int'>
<class 'str'>
['__abs__', '__add__', '__and__', '__bool__', '__ceil__', '__class__', '__delattr__', '__dir__', '__divmod__', '__doc__', '__eq__', '__float__', '__floor__', '__floordiv__', '__format__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__init__', '__init_subclass__', '__int__', '__invert__', '__le__', '__lshift__', '__lt__', '__mod__', '__mul__', '__ne__', '__neg__', '__new__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__round__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'bit_length', 'conjugate', 'denominator', 'from_bytes', 'imag', 'numerator', 'real', 'to_bytes']

Python supports addition (+), substraction(-), multiplication(*), division(/),exponentiation(**), quotient (//) and remainder(%). You can chain exponentiations together. In other words, you can rise a number to multiple powers.

id() function

The id() function returns identity (unique integer) of an object. 

print('id of 5 =',id(5))

a = 5
print('id of a =',id(a))

b = a
print('id of b =',id(b))

c = 5.0
print('id of c =',id(c))

id of 5 = 94364870744704
id of a = 94364870744704
id of b = 94364870744704
id of c = 140097885531312

It's important to note that everything in Python is an object, even numbers, and Classes. Hence, integer 5 has a unique id. The id of the integer 5 remains constant during the lifetime. Similar is the case for float 5.5 and other objects.

isinstance() function

To verify the type of an object, the isinstance() function checks if the object (first argument) is an instance or subclass of classinfo class (second argument).

The None Object

The None object is used to represent the absence of a value. It is similar to null in other programming languages. The None object is returned by any function that doesn't explicitly return anything else.