# antipatterns

Things to avoid in your code

# Definition

An anti-pattern is something that:

• people frequently write in their code (that’s the pattern part)
• but that is BAD and should NOT BE DONE (that’s the anti part).

(The term anti-pattern does have a more formal definition in Computer Science and some history; for purposes of CS8, we’ll focus on the informal definition above.)

This page is here as a place to collect some common anti-patterns often seen in code written by folks new to Python programming (e.g. code submitted by CS8 students in programming assignments, or answers to exam questions.)

There are various kinds of anti-patterns:

• In some cases, the code “works” in the sense that it “computes the correct result”, but it is hard to read for other programmers, or difficult to maintain, or might lead to later bugs or errors.

• Other times it is just wasteful, in that it takes up space in the code for no good reason.

• And sometimes, it is just code that might “seem right”, but is just plain wrong.

# Example

One example that occurs frequently is the explicit use of return true; and return false; after evaluating a boolean expression.


def xIsNegative(x):
if x<0:
return True
else:
return False



The entire if statement here is completely unnecessary. It is far more clear to simply write:

def xIsNegative(x):
return x<0


## The useless else branch

Consider this code for counting the number of times that the value k occurs:

  if a[i] == k:
count = count + 1
else:
count = count + 0


So, this might seem to make sense if you think that you always need an else with an if. But, the else part here is useless! Adding 0 to a variable does nothing! Just write this, with no else clause:

  if a[i] == k:
count = count + 1


Another variation of this antipattern is the x=x; assignment, like this:

  if a[i]  % 2 != 0:
sumEvens = sumEvens + a[i]
else:
sumEvens = sumEvens


Leave off this useless else clause. The variable sumEvens will retain its value without you copying it back onto itself everytime through the code.

# Formal Definition of Anti-Pattern

A more formal definition, from Wikipedia:

An anti-pattern (or antipattern) is a common response to a recurring problem that is usually ineffective and risks being highly counterproductive.[1][2]

The term, coined in 1995 by Andrew Koenig,[3] was inspired by a book, Design Patterns, in which the authors highlighted a number of design patterns in software development that they considered to be highly reliable and effective. The term was popularized three years later by the book AntiPatterns, which extended its use beyond the field of software design and into general social interaction and may be used informally to refer to any commonly reinvented but bad solution to a problem. Examples include analysis paralysis, cargo cult programming, death march, groupthink and vendor lock-in.