Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cyclomatic Complexity

Cyclomatic Complexity corresponds to the number of decisions a block of code contains plus 1. This number (also called McCabe number) is equal to the number of linearly independent paths through the code. This number can be used as a guide when testing conditional logic in blocks.

Radon analyzes the AST tree of a Python program to compute Cyclomatic Complexity. Statements have the following effects on Cyclomatic Complexity:

Source: http://radon.readthedocs.org/en/latest/intro.html

Cyclomatic Complexity

Cyclomatic Complexity corresponds to the number of decisions a block of code contains plus 1. This number (also called McCabe number) is equal to the number of linearly independent paths through the code. This number can be used as a guide when testing conditional logic in blocks.

Radon analyzes the AST tree of a Python program to compute Cyclomatic Complexity. Statements have the following effects on Cyclomatic Complexity:

Source: http://radon.readthedocs.org/en/latest/intro.html

Cognitive Complexity is a measure of how hard the control flow of a function is to understand. Functions with high Cognitive Complexity will be difficult to maintain.

See

• Cognitive Complexity

Used when a function or method has too many return statement, making it hard to follow.

Used when a function or method has too many statements. You should then split it in smaller functions / methods.

Used when class has too few public methods, so be sure it's really worth it.

Used in order to highlight an unnecessary block of code following an if containing a return statement. As such, it will warn when it encounters an else following a chain of ifs, all of them containing a return statement.

Used when a function or method has too many branches, making it hard to follow.

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if condition1:
    if condition2:
        # ...

Compliant Solution

if condition1 and condition2:
    # ...

Having two branches in the same if structure with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then they should be combined.

Noncompliant Code Example

if 0 <= a < 10:
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
elif 20 <= a < 50:
    do_the_thing()  # Noncompliant; duplicates first condition
else:
    do_the_rest()

b = 4 if a > 12 else 4

Compliant Solution

if (0 <= a < 10) or (20 <= a < 50):
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
else:
    do_the_rest()

b = 4

or

if 0 <= a < 10:
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
elif 20 <= a < 50:
    do_the_third_thing()
else:
    do_the_rest()

b = 8 if a > 12 else 4

Most of the time a block of code is empty when a piece of code is really missing. So such empty block must be either filled or removed.

Noncompliant Code Example

for i in range(3):
    pass

Exceptions

When a block contains a comment, this block is not considered to be empty.

Having two branches in the same if structure with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then they should be combined.

Noncompliant Code Example

if 0 <= a < 10:
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
elif 20 <= a < 50:
    do_the_thing()  # Noncompliant; duplicates first condition
else:
    do_the_rest()

b = 4 if a > 12 else 4

Compliant Solution

if (0 <= a < 10) or (20 <= a < 50):
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
else:
    do_the_rest()

b = 4

or

if 0 <= a < 10:
    do_the_thing()
elif 10 <= a < 20:
    do_the_other_thing()
elif 20 <= a < 50:
    do_the_third_thing()
else:
    do_the_rest()

b = 8 if a > 12 else 4

TODO and word[-3] in self._li ^ |

TODO 'ent', ^ |

TODO 'ous', ^ |

TODO 'ive', ^ |

TODO and word[-4] == 'l' ^ |

TODO 'ence', ^ |

TODO 'ment', ^ |

TODO and not self.sbendsinshort_syllable(word[:-1]) ^ |

TODO and word[-1] in {'Y', 'y'} ^ |

TODO 'ic', ^ |

TODO r1_start >= 1 ^ |

TODO 'ance', ^ |

TODO 'ate', ^ |

TODO 'ism', ^ |

TODO len(word[r2_start:]) >= 3 ^ |

TODO len(word[r1_start:]) >= 1 ^ |

TODO 'al', ^ |

TODO 'able', ^ |

TODO and len(word[r1_start:]) >= 2 ^ |

TODO len(word) > 2 ^ |

TODO and len(word) >= 4 ^ |

TODO 'ant', ^ |

TODO 'er', ^ |

TODO and word[-4] in tuple('st') ^ |

TODO 'iti', ^ |

TODO r1_start >= 1 ^ |

TODO 'ible', ^ |

TODO 'ize', ^ |

TODO and word[-2] not in self._vowels ^ |

TODO and len(word[r1_start:]) >= 3 ^ |

TODO 'ement', ^ |

Emitted when code that iterates with range and len is encountered. Such code can be simplified by using the enumerate builtin.