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Python - Variables

 ·   ·  β˜• 6 min read

    Variables are nothing but reserved memory locations to store values. It means that when you create a variable, you reserve some space in the memory.

    Assigning Values to Variables

    Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables.

    The operand to the left of the = operator is the name of the variable and the operand to the right of the = operator is the value stored in the variable. For example βˆ’

    counter = 100          # An integer assignment
    miles   = 1000.0       # A floating point
    name    = "John"       # A string
    print (counter)
    print (miles)
    print (name)

    Multiple Assignment

    Python allows you to assign a single value to several variables simultaneously.

    For example βˆ’

    a = b = c = 1

    Here, an integer object is created with the value 1, and all the three variables are assigned to the same memory location. You can also assign multiple objects to multiple variables. For example βˆ’

    a, b, c = 1, 2, "john"

    Here, two integer objects with values 1 and 2 are assigned to the variables a and b respectively, and one string object with the value “john” is assigned to the variable c.

    Standard Data Types

    The data stored in memory can be of many types. For example, a person’s age is stored as a numeric value and his or her address is stored as alphanumeric characters. Python has various standard data types that are used to define the operations possible on them and the storage method for each of them.

    Python has five standard data types βˆ’

    • Numbers
    • String
    • List
    • Tuple
    • Dictionary

    Python Numbers

    Number data types store numeric values. Number objects are created when you assign a value to them. For example βˆ’

    var1 = 1
    var2 = 10

    You can also delete the reference to a number object by using the del statement. The syntax of the del statement is βˆ’

    del var1[,var2[,var3[....,varN]]]]

    You can delete a single object or multiple objects by using the del statement.

    For example βˆ’

    del var
    del var_a, var_b

    Python supports three different numerical types βˆ’

    • int (signed integers)
    • float (floating point real values)
    • complex (complex numbers)

    All integers in Python3 are represented as long integers. Hence, there is no separate number type as long.

    A complex number consists of an ordered pair of real floating-point numbers denoted by x + yj, where x and y are real numbers and j is the imaginary unit.

    Python Strings

    Strings in Python are identified as a contiguous set of characters represented in the quotation marks. Python allows either pair of single or double quotes. Subsets of strings can be taken using the slice operator ([ ] and [:] ) with indexes starting at 0 in the beginning of the string and working their way from -1 to the end.

    The plus (+) sign is the string concatenation operator and the asterisk (*) is the repetition operator. For example βˆ’

    str = 'Hello World!'
    print (str)          # Prints complete string
    print (str[0])       # Prints first character of the string
    print (str[2:5])     # Prints characters starting from 3rd to 5th
    print (str[2:])      # Prints string starting from 3rd character
    print (str * 2)      # Prints string two times
    print (str + "TEST") # Prints concatenated string

    Python Lists

    Lists are the most versatile of Python’s compound data types. A list contains items separated by commas and enclosed within square brackets ([]). To some extent, lists are similar to arrays in C. One of the differences between them is that all the items belonging to a list can be of different data type.

    The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list and working their way to end -1. The plus (+) sign is the list concatenation operator, and the asterisk (*) is the repetition operator. For example βˆ’

    list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
    tinylist = [123, 'john']
    print (list)          # Prints complete list
    print (list[0])       # Prints first element of the list
    print (list[1:3])     # Prints elements starting from 2nd till 3rd 
    print (list[2:])      # Prints elements starting from 3rd element
    print (tinylist * 2)  # Prints list two times
    print (list + tinylist) # Prints concatenated lists

    Python Tuples

    A tuple is another sequence data type that is similar to the list. A tuple consists of a number of values separated by commas. Unlike lists, however, tuples are enclosed within parenthesis.

    The main difference between lists and tuples are βˆ’ Lists are enclosed in brackets ( [ ] ) and their elements and size can be changed, while tuples are enclosed in parentheses ( ( ) ) and cannot be updated. Tuples can be thought of as read-only lists. For example βˆ’

    tuple = ( 'abcd', 786 , 2.23, 'john', 70.2  )
    tinytuple = (123, 'john')
    print (tuple)           # Prints complete tuple
    print (tuple[0])        # Prints first element of the tuple
    print (tuple[1:3])      # Prints elements starting from 2nd till 3rd 
    print (tuple[2:])       # Prints elements starting from 3rd element
    print (tinytuple * 2)   # Prints tuple two times
    print (tuple + tinytuple) # Prints concatenated tuple

    Python Dictionary

    Python’s dictionaries are kind of hash-table type. They work like associative arrays or hashes found in Perl and consist of key-value pairs. A dictionary key can be almost any Python type, but are usually numbers or strings. Values, on the other hand, can be any arbitrary Python object.

    Dictionaries are enclosed by curly braces ({ }) and values can be assigned and accessed using square braces ([]). For example βˆ’

    dict = {}
    dict['one'] = "This is one"
    dict[2]     = "This is two"
    tinydict = {'name': 'john','code':6734, 'dept': 'sales'}
    print (dict['one'])       # Prints value for 'one' key
    print (dict[2])           # Prints value for 2 key
    print (tinydict)          # Prints complete dictionary
    print (tinydict.keys())   # Prints all the keys
    print (tinydict.values()) # Prints all the values

    Data Type Conversion

    Sometimes, you may need to perform conversions between the built-in types. To convert between types, you simply use the type-names as a function.

    There are several built-in functions to perform conversion from one data type to another. These functions return a new object representing the converted value.

    int(x [,base]): Converts x to an integer. The base specifies the base if x is a string.

    float(x): Converts x to a floating-point number.

    complex(real [,imag]): Creates a complex number.

    str(x): Converts object x to a string representation.

    repr(x): Converts object x to an expression string.

    eval(str): Evaluates a string and returns an object.

    tuple(s): Converts s to a tuple.

    list(s): Converts s to a list.

    set(s): Converts s to a set.

    dict(d): Creates a dictionary. d must be a sequence of (key,value) tuples.

    frozenset(s): Converts s to a frozen set.

    chr(x): Converts an integer to a character.

    unichr(x): Converts an integer to a Unicode character.

    ord(x): Converts a single character to its integer value.

    hex(x): Converts an integer to a hexadecimal string.

    oct(x): Converts an integer to an octal string.

    Ohidur Rahman Bappy
    Ohidur Rahman Bappy
    πŸ“šLearner 🐍 Developer