Operators and Expressions

Read this to learn more about operators and expressions.

We will briefly take a look at the operators and their usage.

Note that you can evaluate the expressions given in the examples using the interpreter interactively. For example, to test the expression 2 + 3, use the interactive Python interpreter prompt:

>>> 2 + 3
5
>>> 3 * 5
15
>>>

Here is a quick overview of the available operators:

  • +  (plus)

    • Adds two objects
    • 3 + 5  gives  8 .  'a' + 'b'  gives  'ab' .

  • -  (minus)

    • Gives the subtraction of one number from the other; if the first operand is absent it is assumed to be zero.
    • -5.2  gives a negative number and 50 - 24  gives  26 . 

  • *  (multiply)

    • Gives the multiplication of the two numbers or returns the string repeated that many times.
    • 2 * 3  gives  6. 'la' * 3  gives  'lalala' .
  • ** (power)
    • Returns x to the power of y
    • 3 ** 4 gives 81 (i.e. 3 * 3 * 3 * 3)

  • / (divide)

    • Divide x by y
    • 13 / 3 gives 4.333333333333333

  • // (divide and floor)

    • Divide x by y and round the answer down to the nearest integer value. Note that if one of the values is a float, you'll get back a float.
    • 13 // 3 gives 4
    • -13 // 3 gives -5
    • 9//1.81 gives 4.0

  • % (modulo)

    • Returns the remainder of the division
    • 13 % 3 gives 1. -25.5 % 2.25 gives 1.5.

  • << (left shift)

    • Shifts the bits of the number to the left by the number of bits specified. (Each number is represented in memory by bits or binary digits i.e. 0 and 1)
    • 2 << 2 gives 8. 2 is represented by 10 in bits.
    • Left shifting by 2 bits gives 1000 which represents the decimal 8.

  • >> (right shift)

    • Shifts the bits of the number to the right by the number of bits specified.
    • 11 >> 1 gives 5.
    • 11 is represented in bits by 1011 which when right shifted by 1 bit gives 101which is the decimal 5.

  • & (bit-wise AND)

    • Bit-wise AND of the numbers: if both bits are 1, the result is 1. Otherwise, it's 0.
    • 5 & 3 gives 1 (0101 & 0011 gives 0001)

  • | (bit-wise OR)

    • Bitwise OR of the numbers: if both bits are 0, the result is 0. Otherwise, it's 1.
    • 5 | 3 gives 7 (0101 | 0011 gives 0111)

  • ^ (bit-wise XOR)

    • Bitwise XOR of the numbers: if both bits (1 or 0) are the same, the result is 0. Otherwise, it's 1.
    • 5 ^ 3 gives 6 (O101 ^ 0011 gives 0110)

  • ~ (bit-wise invert)

  • < (less than)

    • Returns whether x is less than y. All comparison operators return True or False. Note the capitalization of these names.
    • 5 < 3 gives False and 3 < 5 gives True.
    • Comparisons can be chained arbitrarily: 3 < 5 < 7 gives True.

  • > (greater than)

    • Returns whether x is greater than y
    • 5 > 3 returns True. If both operands are numbers, they are first converted to a common type. Otherwise, it always returns False.

  • <= (less than or equal to)

    • Returns whether x is less than or equal to y
    • x = 3; y = 6; x <= y returns True

  • >= (greater than or equal to)

    • Returns whether x is greater than or equal to y
    • x = 4; y = 3; x >= 3 returns True

  • == (equal to)

    • Compares if the objects are equal
    • x = 2; y = 2; x == y returns True
    • x = 'str'; y = 'stR'; x == y returns False
    • x = 'str'; y = 'str'; x == y returns True

  • != (not equal to)

    • Compares if the objects are not equal
    • x = 2; y = 3; x != y returns True

  • not (boolean NOT)

    • If x is True, it returns False. If x is False, it returns True.
    • x = True; not x returns False.

  • and (boolean AND)

    • x and y returns False if x is False, else it returns evaluation of y
    • x = False; y = True; x and y returns False since x is False. In this case, Python will not evaluate y since it knows that the left hand side of the 'and' expression is  False which implies that the whole expression will be False irrespective of the other values. This is called short-circuit evaluation.

  • or (boolean OR)

    • If x is True, it returns True, else it returns evaluation of y
    • x = True; y = False; x or y returns True. Short-circuit evaluation applies here as well.