Trouble with for loops and lists

Question

I'm making a function that puts together a 3d list called param_list. In the last for loop of the function, all the list values are what I want them to be, but then right outside the loop the values are wrong

def make_param_combos( params ):
   size = []
   param_list = []
   temp_params = []
   one_param = ['param','value']
   num_params = len( params )

   for j in range( num_params ) :

      if j == 0 :
        size.append( len(params[j][1] ) )
      else :
        size.append( len(params[j][1]) * size[j-1] ) 
        num_combos = size[j]

   for i in range( num_combos ) :

      temp_params.clear()

      for j in range( num_params ) :

         one_param = [ params[j][0], params[j][1][ int( np.mod( len( params[j][1] ) * i/size[j], len( params[j][1] ) ) ) ] ]

         temp_params.append( one_param )  

      param_list.append( temp_params )

      print( "loop iter", i, param_list[i] )

   print( "out of loop" )
   print( param_list )

   return param_list



plist = make_param_combos([[['param1'],['v11','v12']],[['param2'],['v21','v22']],[['param3'],['v31','v32']]]) 

print( "out of function" )

for i in range(len(plist)):
  print(plist[i])

the result:

loop iter 0 [[['param1'], 'v11'], [['param2'], 'v21'], [['param3'], 'v31']] loop iter 1 [[['param1'], 'v12'], [['param2'], 'v21'], [['param3'], 'v31']]

loop iter 2 [[['param1'], 'v11'], [['param2'], 'v22'], [['param3'], 'v31']]

loop iter 3 [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v31']]

loop iter 4 [[['param1'], 'v11'], [['param2'], 'v21'], [['param3'], 'v32']]

loop iter 5 [[['param1'], 'v12'], [['param2'], 'v21'], [['param3'], 'v32']]

loop iter 6 [[['param1'], 'v11'], [['param2'], 'v22'], [['param3'], 'v32']]

loop iter 7 [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

out of loop [[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']], [[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]]

out of function

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

[[['param1'], 'v12'], [['param2'], 'v22'], [['param3'], 'v32']]

Answer 1

Replace temp_params.clear() with temp_params = []. You need a new list, .clear() will delete all elements from the old list - the one you have just appended to param_list. You have appended this list, the one you're clearing now, not its copy.