如何从包含其名称的字符串中选择一个变量？

Question

So I am trying to get a loop function to automatically identify the next list to append a number. The following sample code summarizes what I am trying to achieve.

start = 'patch'
end = 'List'

patch1List = []; patch2List = []; patch3List = []; patch4List = []; patch5List = []; patch6List = []
patch7List = []; patch8List = []; patch9List = []; patch10List = []

for patch in range(10):
    num = patch+1
    DataPoint = random.randint(1,10)

    currentPList = ('%s%d%s' % (start,num,end))
    currentPList.append(DataPoint)

I need the loop to append a data point into each of the 10 empty lists.

I tried to do this by setting up currentPList to identify the list to work with. The problem is, I am not quite sure how to convert currentPList , which is currently a string, into a proper object (ie. one of the empty patchList s). How do I go about doing this?

Answer 1

You are definitely overcomplicating this. Just use a list of lists:

>>> import random
>>> num_arrays = 10
>>> array = [ [random.randint(1,10)] for i in range(num_arrays) ]
>>> array
[[2], [1], [10], [6], [9], [2], [2], [5], [8], [4]]

This way you can get the same functionality of each individual list and have it be extensible and not try to reference a variable by a concatenated string for its name.

Answer 2

@Charles Drotar's answer is what you want to do, but since the title says how to convert a string to variable name, here is how you can actually create variables specified as strings (but don't do this in your circumstance):

s = 'string'
for i in range(1,6):
    vars().update({s + str(i): i})

>>> string2
2
>>> string5
5

What you are doing here is adding the variable entry to the namespace. In the absence of an object argument vars() acts like locals()

Answer 3

I think the Pythonic way to do it would be to store all the patch lists a single dictionary. That way you can easily select which one by creating a unique dictionary key for each of them. Note also that the keys generated don't even need to be valid Python identifiers using this approach—and it would be very easy to change how many there were, since it's all done dynamically.

Here's what I mean (Note I also made the variable names used following the PEP 8 Naming Conventions ):

from collections import defaultdict
import random

START, END = 'patch', 'List'
patches = defaultdict(list)  # A dictionary whose values default to lists.

for patch_num in range(1, 11):
    data_point = random.randint(1, 10)
    current_patch_list = ('%s%d%s' % (START, patch_num, END))  # Create key.
    patches[current_patch_list].append(data_point)

print(dict(patches))

Sample utput:

{'patch1List': [5], 'patch2List': [8], 'patch3List': [4], 'patch4List': [9], 'patch5List': [10], 'patch6List': [9], 'patch7List': [5], 'patch8List': [9], 'patch9List': [8], 'patch10List': [7]}