Automatically simplifying/refactoring Python code (e.g. for loops - list comprehension)? [closed]
2024/9/19 9:09:43
In Python, I really enjoy how concise an implementation can be when using list comprehension. I love to do concise list comprehensions this:
myList = [1, 5, 11, 20, 30, 35] #input data
bigNumbers = [x for x in myList if x > 10]
However, I often encounter more verbose implementations like this:
myList = [1, 5, 11, 20, 30, 35] #input data
bigNumbers = []
for i in xrange(0, len(myList)):if myList[i] > 10:bigNumbers.append(myList[i])
When a for loop only looks through one data structure (e.g. myList[]), there is usually a straightforward list comprehension statement that is equivalent to the loop. With this in mind, is there a refactoring tool that converts verbose Python loops into concise list comprehension statements?
Previous StackOverflow questions have asked for advice on transforming loops into list comprehension. But, I have yet to find a question about automatically converting loops into list comprehension expressions.
Motivation: There are numerous ways to answer the question "what does it mean for code to be clean?" Personally, I find that making code concise and getting rid of some of the fluff tends to make code cleaner and more readable. Naturally there's a line in the sand between "concise code" and "incomprehensible one-liners." Still, I often find it satisfying to write and work with concise code.
Answer
2to3 is a refactoring tool that can perform arbitrary refactorings, as long as you can specify them with a syntactical pattern. The pattern you might want to look for is this
VARIABLE1 = []
for VARIABLE2 in EXPRESSION1:if EXPRESSION2:VARIABLE1.append(EXPRESSION3)
This can be refactored safely to
VARIABLE1 = [EXPRESSION3 for VARIABLE2 in EXPRESSION1 if EXPRESSION2]
In your specific example, this would give
bigNumbers = [myList[i] for i in xrange(0, len(myList)) if myList[i] > 10]
Then, you can have another refactoring that replaces xrange(0, N) with xrange(N),
and another one that replaces
[VARIABLE1[VARIABLE2] for VARIABLE2 in xrange(len(VARIABLE1)) if EXPRESSION1]
with
[VARIABLE3 for VARIABLE3 in VARIABLE1 if EXPRESSION1PRIME]
There are several problems with this refactoring:
EXPRESSION1PRIME must be EXPRESSION1 with all occurrences of
VARIABLE1[VARIABLE2] replaced by VARIABLE3. This is possible with
2to3, but requires explicit code to do the traversal and replacement.
EXPRESSION1PRIME then must not contain no further occurrences of
VARIABLE1. This can also be checked with explicit code.
One needs to come up with a name for VARIABLE3. You have chosen x;
there is no reasonable way to have this done automatically. You could
chose to recycle VARIABLE1 (i.e. i) for that, but that may be confusing
as it suggests that i is still an index. It might work to pick a synthetic
name, such as VARIABLE1_VARIABLE2 (i.e. myList_i), and check whether
that's not used otherwise.
One needs to be sure that VARIABLE1[VARIABLE2] yields the same as you get
when using iter(VARIABLE1). It's not possible to do this automatically.
If you want to learn how to write 2to3 fixers, take a look at Lennart Regebro's book.
I am trying to optimize an SVR model and facing a problem because of overfitting, to overcome this I have tried to decrease the number of iterations instead of leaving it until convergence.To compare …
What is the reason that NaNs are considered less than -np.inf in any comparisons involving np.min or np.argmin?import numpy as np
In [73]: m = np.array([np.nan, 1., 0., -np.inf])
In [74]: n = np.array…
I am trying to place a recursive formula inside a class statementclass SomeNode:def __init__(self, a):leng = len(a)half= leng/2self.firstnode=a[0][0]self.child1=SomeNode([a[i]for k in range(leng)])self…
Im trying to use spyne (http://spyne.io) in my server with ZeroMQ and MsgPack. Ive followed the examples to program the server side, but i cant find any example that helps me to know how to program the…
This question already has answers here:What is the difference between a function, an unbound method and a bound method?(6 answers)Closed 5 years ago.I know I can attach a function to a class and make …
can someone help me with a little cropping algorithm? its openCV.. im trying to figure this out. I know the method is crop = image[y:y1, x:x1].
If I have an image with new_dimensionXxnew_dimensionY pi…
Im training a U-Net CNN in Keras/Tensorflow and find that loss massively decreases between the last batch of the first epoch, and the first batch of the second epoch:
Epoch 00001: loss improved from in…
I have a project where I am given a file and i need to extract the strings from the file. Basically think of the "strings" command in linux but im doing this in python. The next condition is …
Is there a way to install numpy on a Mac so that it will work when uploaded to AWS Lambda? I have tried a variety of different ways, including using different pip versions, using easy_install, and fol…
I want to run a function for 10s then do other stuff. This is my code using Timerfrom threading import Timer
import timedef timeout():b=truereturn ba=false
t = Timer(10,timeout)
t.start()while(a==f…