Understanding Operators and Expressions

Operators inform Python that a computation is to be performed. For instance, to add two numbers, the syntax would be:

>>> 2 + 5

7

Here, the plus sign (+) is the operator, and the values it acts upon are the operands. Instead of using literal values, identifiers can also serve as operands:

>>> a = 2

>>> b = 5

>>> a + b

7

This series of commands is known as an expression, which combines operators and operands to yield a singular value.

Arithmetic Operators

Let's examine how arithmetic operators function in Python:

>>> a = -2

>>> b = 7

>>> -a  # Two negatives should yield a positive

2

>>> a + b

5

>>> a - b

-9

>>> a * b

-14

>>> -b * a  # Multiplying two negatives should yield a positive

14

>>> b / -a

3.5

>>> b % -a

1

>>> b // -a

3

>>> b ** a

0.02040816326530612

It's notable that standard division with / consistently produces a float value:

>>> 15 / 3

5.0

When performing floor division, Python truncates the fractional part for positive numbers:

>>> 7 // 2

3

For negative numbers, it rounds down, which can lead to unexpected results:

>>> 7 // -2

-4

Relational Operators

Relational operators, also known as comparison operators, allow for the evaluation of conditions:

>>> a = 2

>>> b = 4

>>> a == b

False

>>> a != b

True

>>> a < b

True

>>> a > b

False

>>> a <= b

True

These operators are essential for controlling program flow through conditional statements. They help execute specific code based on whether conditions are met:

if a > b:

# Execute some code

Mind the Gotcha

When comparing floating-point values, accuracy may become an issue:

>>> a = 2.2 + 3.6

>>> a == 5.8

False

Due to how floating-point numbers are represented in memory, it's better to check for equality using a tolerance level:

>>> tol = 1e-5

>>> abs(a - 5.8) < tol

True

Logical Operators

Logical operators join and modify expressions within a boolean context, requiring evaluations to be either True or False. They enable the creation of complex conditions:

>>> if a > 0 and b > 0:

print("a and b are both greater than 0")

For the and operator, both conditions must be true for the result to be True. The not operator inverses the boolean value:

>>> a = False

>>> if not a:

print("It gets confusing")

The or operator requires at least one condition to be true:

>>> if a > 0 or b > 0:

print("At least one is greater than 0")

Order of Precedence

Recall the BIDMAS (or BODMAS) rule from school? Python follows a similar order of operations to ensure clarity when multiple operators are involved. Operators with higher precedence are computed first, working down to those with lower precedence.

This tutorial has focused on the most frequently used operators in Python, but numerous others exist. For those interested in a deeper understanding, I recommend further reading on Python Operators and Expressions.

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