[Python] Does loc/iloc return a reference or a copy?

I am experiencing some problems while using .loc / .iloc as part of a loop. This is a simplified version of my code:


INDEX=['0', '1', '2', '3', '4']
COLUMNS=['A','B','C']
df=pd.DataFrame(index=INDEX, columns=COLUMNS)
i=0

while i<1000:

for row in INDEX:
df.loc[row] = function()
#breakpoint

i_max = df['A'].idxmax()
row_MAX=df.loc[i_max]

if i == 0:
row_GLOBALMAX=row_MAX
elif row_MAX > row_GLOBALMAX:
row_GLOBALMAX=row_MAX

i+=1


basically:

1. 
   I initialize a dataframe with index and columns
   
   
2. 
   I populate each row of the dataframe with a for loop
   
   
3. 
   I find the index "i_max" finding the maximum value in column 'A'
   
   
4. 
   I save the row of the dataframe where the value is maximum 'row_MAX'
   
   
5. 
   The while loop iterates over steps 2 to 4 and uses a new variable row_GLOBALMAX to save the row with the highest value in row 'A'
   

The code works as expected during the first execution of the while loop (i=0), however at the second iteration (i=1) when I stop at the indicated breakpoint I observe a problem: both 'row_MAX' and 'row_GLOBALMAX' have already changed with respect to the first iteration and have followed the values in the updated 'df' dataframe, even though I haven't yet assigned them in the second iteration.

basically it seems like the .loc function created a pointer to a particular row of the 'df' dataframe instead of actually assigning a value in that particular moment. Is this the normal behaviour? What should I use instead of .loc?

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