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

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

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 34.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Use indent_size (PEP8 says 4) spaces per indentation level.

For really old code that you don't want to mess up, you can continue
to use 8-space tabs.

Okay: a = 1
Okay: if a == 0:\n    a = 1
E111:   a = 1
E114:   # a = 1

Okay: for item in items:\n    pass
E112: for item in items:\npass
E115: for item in items:\n# Hi\n    pass

Okay: a = 1\nb = 2
E113: a = 1\n    b = 2
E116: a = 1\n    # b = 2

Continuation lines indentation.

Continuation lines should align wrapped elements either vertically
using Python's implicit line joining inside parentheses, brackets
and braces, or using a hanging indent.

When using a hanging indent these considerations should be applied:
- there should be no arguments on the first line, and
- further indentation should be used to clearly distinguish itself
  as a continuation line.

Okay: a = (\n)
E123: a = (\n    )

Okay: a = (\n    42)
E121: a = (\n   42)
E122: a = (\n42)
E123: a = (\n    42\n    )
E124: a = (24,\n     42\n)
E125: if (\n    b):\n    pass
E126: a = (\n        42)
E127: a = (24,\n      42)
E128: a = (24,\n    42)
E129: if (a or\n    b):\n    pass
E131: a = (\n    42\n 24)

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Separate inline comments by at least two spaces.

An inline comment is a comment on the same line as a statement.
Inline comments should be separated by at least two spaces from the
statement. They should start with a # and a single space.

Each line of a block comment starts with a # and a single space
(unless it is indented text inside the comment).

Okay: x = x + 1  # Increment x
Okay: x = x + 1    # Increment x
Okay: # Block comment
E261: x = x + 1 # Increment x
E262: x = x + 1  #Increment x
E262: x = x + 1  #  Increment x
E265: #Block comment
E266: ### Block comment

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Continuation lines indentation.

Continuation lines should align wrapped elements either vertically
using Python's implicit line joining inside parentheses, brackets
and braces, or using a hanging indent.

When using a hanging indent these considerations should be applied:
- there should be no arguments on the first line, and
- further indentation should be used to clearly distinguish itself
  as a continuation line.

Okay: a = (\n)
E123: a = (\n    )

Okay: a = (\n    42)
E121: a = (\n   42)
E122: a = (\n42)
E123: a = (\n    42\n    )
E124: a = (24,\n     42\n)
E125: if (\n    b):\n    pass
E126: a = (\n        42)
E127: a = (24,\n      42)
E128: a = (24,\n    42)
E129: if (a or\n    b):\n    pass
E131: a = (\n    42\n 24)

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Use indent_size (PEP8 says 4) spaces per indentation level.

For really old code that you don't want to mess up, you can continue
to use 8-space tabs.

Okay: a = 1
Okay: if a == 0:\n    a = 1
E111:   a = 1
E114:   # a = 1

Okay: for item in items:\n    pass
E112: for item in items:\npass
E115: for item in items:\n# Hi\n    pass

Okay: a = 1\nb = 2
E113: a = 1\n    b = 2
E116: a = 1\n    # b = 2

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Continuation lines indentation.

Continuation lines should align wrapped elements either vertically
using Python's implicit line joining inside parentheses, brackets
and braces, or using a hanging indent.

When using a hanging indent these considerations should be applied:
- there should be no arguments on the first line, and
- further indentation should be used to clearly distinguish itself
  as a continuation line.

Okay: a = (\n)
E123: a = (\n    )

Okay: a = (\n    42)
E121: a = (\n   42)
E122: a = (\n42)
E123: a = (\n    42\n    )
E124: a = (24,\n     42\n)
E125: if (\n    b):\n    pass
E126: a = (\n        42)
E127: a = (24,\n      42)
E128: a = (24,\n    42)
E129: if (a or\n    b):\n    pass
E131: a = (\n    42\n 24)

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Compound statements (on the same line) are generally discouraged.

While sometimes it's okay to put an if/for/while with a small body
on the same line, never do this for multi-clause statements.
Also avoid folding such long lines!

Always use a def statement instead of an assignment statement that
binds a lambda expression directly to a name.

Okay: if foo == 'blah':\n    do_blah_thing()
Okay: do_one()
Okay: do_two()
Okay: do_three()

E701: if foo == 'blah': do_blah_thing()
E701: for x in lst: total += x
E701: while t < 10: t = delay()
E701: if foo == 'blah': do_blah_thing()
E701: else: do_non_blah_thing()
E701: try: something()
E701: finally: cleanup()
E701: if foo == 'blah': one(); two(); three()
E702: do_one(); do_two(); do_three()
E703: do_four();  # useless semicolon
E704: def f(x): return 2*x
E731: f = lambda x: 2*x

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Trailing blank lines are superfluous.

Okay: spam(1)
W391: spam(1)\n

However the last line should end with a new line (warning W292).

Separate top-level function and class definitions with two blank lines.

Method definitions inside a class are separated by a single blank
line.

Extra blank lines may be used (sparingly) to separate groups of
related functions.  Blank lines may be omitted between a bunch of
related one-liners (e.g. a set of dummy implementations).

Use blank lines in functions, sparingly, to indicate logical
sections.

Okay: def a():\n    pass\n\n\ndef b():\n    pass
Okay: def a():\n    pass\n\n\nasync def b():\n    pass
Okay: def a():\n    pass\n\n\n# Foo\n# Bar\n\ndef b():\n    pass
Okay: default = 1\nfoo = 1
Okay: classify = 1\nfoo = 1

E301: class Foo:\n    b = 0\n    def bar():\n        pass
E302: def a():\n    pass\n\ndef b(n):\n    pass
E302: def a():\n    pass\n\nasync def b(n):\n    pass
E303: def a():\n    pass\n\n\n\ndef b(n):\n    pass
E303: def a():\n\n\n\n    pass
E304: @decorator\n\ndef a():\n    pass
E305: def a():\n    pass\na()
E306: def a():\n    def b():\n        pass\n    def c():\n        pass

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.