# python – Pylint, PyChecker or PyFlakes?

## The Question :

395 people think this question is useful

I would like to get some feedback on these tools on:

• features;
• ease of use and learning curve.
• what tag standard has to do with this?
• Because you use this tools to match PEP, especially PEP 8 which is the standard for all built-in Python modules.
• and what other peps do you want it to match? because for pep-8 there is an unambiguous tag stackoverflow.com/questions/tagged/pep8
• You are right, I’ll switch to pep8
• Shouldn’t the title be edited to include pep8 as an option? At first, I thought you guys were talking about the proposition, not an actual PyPI package.

280 people think this answer is useful

Well, I am a bit curious, so I just tested the three myself right after asking the question 😉

Ok, this is not a very serious review, but here is what I can say:

I tried the tools with the default settings (it’s important because you can pretty much choose your check rules) on the following script:

#!/usr/local/bin/python
# by Daniel Rosengren modified by e-satis

import sys, time
stdout = sys.stdout

BAILOUT = 16
MAX_ITERATIONS = 1000

class Iterator(object) :

def __init__(self):

print 'Rendering...'
for y in xrange(-39, 39):
stdout.write('\n')
for x in xrange(-39, 39):
if self.mandelbrot(x/40.0, y/40.0) :
stdout.write(' ')
else:
stdout.write('*')

def mandelbrot(self, x, y):
cr = y - 0.5
ci = x
zi = 0.0
zr = 0.0

for i in xrange(MAX_ITERATIONS) :
temp = zr * zi
zr2 = zr * zr
zi2 = zi * zi
zr = zr2 - zi2 + cr
zi = temp + temp + ci

if zi2 + zr2 > BAILOUT:
return i

return 0

t = time.time()
Iterator()
print '\nPython Elapsed %.02f' % (time.time() - t)



As a result:

• PyChecker is troublesome because it compiles the module to analyze it. If you don’t want your code to run (e.g, it performs a SQL query), that’s bad.
• PyFlakes is supposed to be light. Indeed, it decided that the code was perfect. I am looking for something quite severe so I don’t think I’ll go for it.
• PyLint has been very talkative and rated the code 3/10 (OMG, I’m a dirty coder !).

Strong points of PyLint:

• Very descriptive and accurate report.
• Detect some code smells. Here it told me to drop my class to write something with functions because the OO approach was useless in this specific case. Something I knew, but never expected a computer to tell me :-p
• The fully corrected code run faster (no class, no reference binding…).
• Made by a French team. OK, it’s not a plus for everybody, but I like it 😉

Cons of Pylint:

• Some rules are really strict. I know that you can change it and that the default is to match PEP8, but is it such a crime to write ‘for x in seq’? Apparently yes because you can’t write a variable name with less than 3 letters. I will change that.

Corrected script (with lazy doc strings and variable names):

#!/usr/local/bin/python
# by Daniel Rosengren, modified by e-satis
"""
Module doctring
"""

import time
from sys import stdout

BAILOUT = 16
MAX_ITERATIONS = 1000

def mandelbrot(dim_1, dim_2):
"""
function doc string
"""
cr1 = dim_1 - 0.5
ci1 = dim_2
zi1 = 0.0
zr1 = 0.0

for i in xrange(MAX_ITERATIONS) :
temp = zr1 * zi1
zr2 = zr1 * zr1
zi2 = zi1 * zi1
zr1 = zr2 - zi2 + cr1
zi1 = temp + temp + ci1

if zi2 + zr2 > BAILOUT:
return i

return 0

def execute() :
"""
func doc string
"""
print 'Rendering...'
for dim_1 in xrange(-39, 39):
stdout.write('\n')
for dim_2 in xrange(-39, 39):
if mandelbrot(dim_1/40.0, dim_2/40.0) :
stdout.write(' ')
else:
stdout.write('*')

START_TIME = time.time()
execute()
print '\nPython Elapsed %.02f' % (time.time() - START_TIME)



Thanks to Rudiger Wolf, I discovered pep8 that does exactly what its name suggests: matching PEP8. It has found several syntax no-nos that Pylint did not. But Pylint found stuff that was not specifically linked to PEP8 but interesting. Both tools are interesting and complementary.

Eventually I will use both since there are really easy to install (via packages or setuptools) and the output text is so easy to chain.

To give you a little idea of their output:

pep8:

./python_mandelbrot.py:4:11: E401 multiple imports on one line
./python_mandelbrot.py:10:1: E302 expected 2 blank lines, found 1
./python_mandelbrot.py:10:23: E203 whitespace before ':'
./python_mandelbrot.py:15:80: E501 line too long (108 characters)
./python_mandelbrot.py:23:1: W291 trailing whitespace
./python_mandelbrot.py:41:5: E301 expected 1 blank line, found 3



Pylint:

************* Module python_mandelbrot
C: 15: Line too long (108/80)
C: 61: Line too long (85/80)
C:  1: Missing docstring
C:  5: Invalid name "stdout" (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$) C: 10:Iterator: Missing docstring C: 15:Iterator.__init__: Invalid name "y" (should match [a-z_][a-z0-9_]{2,30}$)
C: 17:Iterator.__init__: Invalid name "x" (should match [a-z_][a-z0-9_]{2,30}\$)

[...] and a very long report with useful stats like :

Duplication
-----------

+-------------------------+------+---------+-----------+
|                         |now   |previous |difference |
+=========================+======+=========+===========+
|nb duplicated lines      |0     |0        |=          |
+-------------------------+------+---------+-----------+
|percent duplicated lines |0.000 |0.000    |=          |
+-------------------------+------+---------+-----------+