Im trying to create a number of lists depending on the number in my header_count. The code below should generate 3 lists but i get a syntax error instead.
header_count = 4 for i in range(1, header_count): header_%s = [] % i 
5 Answers
This is my interpretation of what you want, I hope I guessed it right (you weren't very clear).
header_count = 4 headers = [[] for i in range(1, header_count)] Now you can use it like this:
headers[1].append("this goes in the first header") headers[2].append("this goes in the second header") 
What you want is to to create a list of lists:
header_count = 4 header = [] for i in range(header_count): header[i] = [] In the header variable references a list containing 4 lists. Each list can be accessed as follow:
header[0].append(1) header[1].append("Hi") header[2].append(3.14) header[3].append(True) 
2 Comments
orlp
header[0].append(1) is a index exception.
Vincenzo Pii
This doesn't work, maybe it should be:
for i in range(1, header_count): header.append([])If you need list names (as it seems from your comment to nightcracker answer), you can use a dictionary of lists:
header_count = 4 listDict = {} for i in range(1, header_count): listDict["header_"+str(i)] = [] Then you can access the dictionary using header_1, header_2, header_3 as keys.
3 Comments
orlp
Please don't encourage bad practices.
Vincenzo Pii
That's what he seemed to have asked for! One can never know, maybe it was a curiosity even if it's a terrible practice.
JoshAdel
A dictionary is the appropriate data structure if the names are dynamically generated and have some information content beyond a simple counter (see the answer to the following question how-can-you-dynamically-create-variables-in-python-via-to-a-while-loop). If the variables names are redundant with a simple count or index, then a list is the appropriate data structure.
You can use global() to create these variables:
header_count = 4 for i in range(1, header_count): globals()[f"header_{i}"] = [] Note: you started your range with value 1, so you will create three empty lists:
header_1 header_2 header_3 
Comments
What did you mean by header_%s? % is the mod operator, of course you can't assign to an expression involving an operator. It's like writing
a+b = c You can't assign to a+b, nor can you assign to header_%s.
Did you mean this?
header_lists = [[] for i in range(1,header_count)] 
header_countto 4. Better to setheader_count = 3and iteratefor i in xrange(header_count).