There is a strange behavior while processing data in a "for" loop with urllib.parse.unquote() - looks like memory corruption - a list contains elements that have never been appended.

I'll explain the testcase.

I spotted the problem by checking for any remains of url encoding left in output_list. There were these strings with url encoding left - "bad_boys" dict in testcase. Now, when iterating through input_list (read from "data.txt"), I'm checking for those problematic entries and printing what is being appended to the output_list as well as all problematic (unwanted, "Bad Boys") and converted problematic entries ("Normal conversions") existing in the output_list. At some point, unwanted entries appear in output_list. The resulting output_list contains converted and unconverted problematic entries, though input_list's length equals output_list's length.

data.txt needs to be saved along with testcase.py, and then you can run testcase.py.

The output of running testcase.py:

Bad Boys are:
	 seil%2fturbo_firmware 140335684191552
	 intelligent_platforms_proficy_hmi%2fscada_cimplicity 140335684515920
	 seil%2fneu_2fe_plus_firmware 140335684536080
	 seil%2fb1_firmware 140335684134640
	 eil%2fx2_firmware 140335684191984
	 seil%2fx1_firmware 140335684190832
	 seil%2fx2_firmware 140335684190904
	 seil%2fx86_firmware 140335684192488

Input list length is: 17094 

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fb1_firmware 140335679096848 >> seil/b1_firmware 140335681345768
Just appended: seil/b1_firmware 140335681345768
Normal conversions in output list:
	 seil/b1_firmware 140335681345768

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fx1_firmware 140335679096920 >> seil/x1_firmware 140335681345840
Just appended: seil/x1_firmware 140335681345840
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fx2_firmware 140335679096992 >> seil/x2_firmware 140335681345912
Just appended: seil/x2_firmware 140335681345912
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fx86_firmware 140335679134936 >> seil/x86_firmware 140335681346704
Just appended: seil/x86_firmware 140335681346704
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912
	 seil/x86_firmware 140335681346704
Bad Boys in output list:
	 eil%2fx2_firmware 140335681346272

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fturbo_firmware 140335679200976 >> seil/turbo_firmware 140335679269456
Just appended: seil/turbo_firmware 140335679269456
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912
	 seil/x86_firmware 140335681346704
	 seil/turbo_firmware 140335679269456
Bad Boys in output list:
	 eil%2fx2_firmware 140335681346272
	 seil%2fb1_firmware 140335679267800
	 seil%2fx1_firmware 140335679267872
	 seil%2fx2_firmware 140335679267944
	 seil%2fx86_firmware 140335679269384

Bad Boy detected
Element type: <class 'str'>
Convertation: seil%2fneu_2fe_plus_firmware 140335678867056 >> seil/neu_2fe_plus_firmware 140335680328928
Just appended: seil/neu_2fe_plus_firmware 140335680328928
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912
	 seil/x86_firmware 140335681346704
	 seil/turbo_firmware 140335679269456
	 seil/neu_2fe_plus_firmware 140335680328928
Bad Boys in output list:
	 eil%2fx2_firmware 140335681346272
	 seil%2fb1_firmware 140335679267800
	 seil%2fx1_firmware 140335679267872
	 seil%2fx2_firmware 140335679267944
	 seil%2fx86_firmware 140335679269384
	 seil%2fturbo_firmware 140335679849576

Bad Boy detected
Element type: <class 'str'>
Convertation: intelligent_platforms_proficy_hmi%2fscada_cimplicity 140335678546800 >> intelligent_platforms_proficy_hmi/scada_cimplicity 140335681194376
Just appended: intelligent_platforms_proficy_hmi/scada_cimplicity 140335681194376
Normal conversions in output list:
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912
	 seil/x86_firmware 140335681346704
	 seil/turbo_firmware 140335679269456
	 seil/neu_2fe_plus_firmware 140335680328928
	 intelligent_platforms_proficy_hmi/scada_cimplicity 140335681194376
Bad Boys in output list:
	 eil%2fx2_firmware 140335681346272
	 seil%2fb1_firmware 140335679267800
	 seil%2fx1_firmware 140335679267872
	 seil%2fx2_firmware 140335679267944
	 seil%2fx86_firmware 140335679269384
	 seil%2fturbo_firmware 140335679849576
	 seil%2fneu_2fe_plus_firmware 140335678934512

FINAL RESULTS
Output list length is: 17094
Normal conversions in output list (Bad Boys -related):
	 seil/b1_firmware 140335681345768
	 seil/x1_firmware 140335681345840
	 seil/x2_firmware 140335681345912
	 seil/x86_firmware 140335681346704
	 seil/turbo_firmware 140335679269456
	 seil/neu_2fe_plus_firmware 140335680328928
	 intelligent_platforms_proficy_hmi/scada_cimplicity 140335681194376
Bad Boys in output list:
	 eil%2fx2_firmware 140335681346272
	 seil%2fb1_firmware 140335679267800
	 seil%2fx1_firmware 140335679267872
	 seil%2fx2_firmware 140335679267944
	 seil%2fx86_firmware 140335679269384
	 seil%2fturbo_firmware 140335679849576
	 seil%2fneu_2fe_plus_firmware 140335678934512
	 intelligent_platforms_proficy_hmi%2fscada_cimplicity 140335681195728