How to access variable with strings?

Question

I am having a problem accessing multiple lists with two criteria: Case_Num and Case_Type. I do not know how to fix the error of concatenate string and lists objects.

I have tried using loops and combing strings and regular integer values.Unfortunatley I keep getting same error. Any help would be appreicated

_2019_case_1=[]

_2019_case_2=[]

_2019_case_3=[]


Case_Num=[2019,2019,2019,2020,2020,2020,2024,2024,2024,2029,2029,2029]
Case_Type=[1,2,3,1,2,3,1,2,3,1,2,3]

dr = "F:\C\FE\CD\Tran\ctg"
read_files =[] 
for root, _, files in os.walk(dr):
    read_files_2="_"+Case_Num+"_case_"+Case_Type 
    for file in files:
        if file in read_files_2:
            read_files.append(os.path.join(root, file))

Error I receive

read_files_2="_"+Case_Num+"_case_"+Case_Type
TypeError: cannot concatenate 'str' and 'list' objects

`Case_Num` and `Case_Type` are lists. What do you expect to happen by adding them to a `str`? — Error - Syntactical Remorse, Jul 09 '19 at 13:39
Use a dictionary instead of encoding information in the variable names → `read_files_2 = cases[(n, t)]` where `n` is one of the `Case_Num`s and `t` is one of the `Case_Type`s. — mkrieger1, Jul 09 '19 at 13:39
Also you should fix your spacing. You should have a space after commas and a space before and after operators (such as `+`). — Error - Syntactical Remorse, Jul 09 '19 at 13:41
Possible duplicate of [How do I create a variable number of variables?](https://stackoverflow.com/questions/1373164/how-do-i-create-a-variable-number-of-variables) — mkrieger1, Jul 09 '19 at 13:41
The longer I read this question, the less I understand what you are trying to do... Please clarify. — mkrieger1, Jul 09 '19 at 13:45

Jab · Answer 1 · 2019-07-09T13:48:52.770

2

You need to change the line where you assign read_files_2 to a set comprehension. And best to just do this once so assign it before the loops. As stated in the comments you can use itertools.product as well for easily extensible changes.

from itertools import product

_2019_case_1=[]

_2019_case_2=[]

_2019_case_3=[]

dr = "F:\C\FE\CD\Tran\ctg"
read_files =[] 
read_files_2= {f"_{num}_case_{type}" for num, type in product((2019,2020,2024,2029), (1,2,3))}
for root, _, files in os.walk(dr): 
    for file in files:
        if file in read_files_2:
            read_files.append(os.path.join(root, file))

edited Jul 09 '19 at 13:48

answered Jul 09 '19 at 13:42

Jab

26,853
21
75
114

you could use `itertools.product` on `[2019,2020,2024,2029]` and `[1,2,3]` to make it a little shorter and readable (and easily extensible to more nums and types) – Adam.Er8 Jul 09 '19 at 13:46
`{f"_{num}_case_{type}" for num, type in product((2019,2020,2024,2029), (1,2,3))}` I get a syntax error with the quotation marks @Jab – joe Jul 09 '19 at 15:05
i do not have Python 3.6 – joe Jul 09 '19 at 15:14
Just use the string concatenation like in your question or str.format – Jab Jul 09 '19 at 15:26
`read_files_2={"_{num}_case_{type}".format(num, type)for num, type in product((2019,2020,2024,2029), (1,2,3))}` I tried this but i get a `KeyError: 'num'` – joe Jul 09 '19 at 15:39

How to access variable with strings?

1 Answers1