关于优化一些嵌套 for 循环的非常菜鸟 Python 问题

Question

I am very new to Python, and have just have just got a small piece of code working to compile some user data into a single file. But since I am only learning, I don't just want it to run, but to actually use the functionality Python provides. For reference, here is the part of the code I think can be made faster.

In short, I have a list of usernames in a text file and usage data for each user over a 4 month period in a CSV for each day.

The logic is

loop over each CSV:
    loop over each line in that CSV:
         loop over the list of usernames:
               if the username matches, append the user data for that user

The inner two for loops are what I am really focussing on improving, since that is where there is a bit of a bottleneck given the number of users. In what follows, username_list is a list that I read from the text file and read_csv is a list that is read from the csv file. The working code is as follows:

#Initialise a dictionary of lists to store the final data and read the keys (which are the usernames)
main_data = {}
with open(".\\listofusernames.txt") as usernames:
     username_list = usernames.read().splitlines()

for user in username_list:
    main_data[user] = []

#Loop over the CSV files with usage data for each day for 3 months
for i in range(1,91):
    csvdir = f".\\csvfiles\\usagedata_{i}.csv"
    with open(csvdir, 'r') as daily_usage_csv:
         read_csv = list(csv.reader(daily_usage_csv))

#Nested loops over the username list and CSV to get the data for the correct user
for user in username_list:
        for line in read_csv:
             #Username is stored in the first column of CSV so we do an if statement on index 0 of the line
             if line[0] == user:
                 #Usage data is in the second and third column of the CSV, so we append index 1 and 2
                 main_data[user].append(line[1])
                 main_data[user].append(line[2])
                 break

The place where I really want to optimise is in the inner two for loops, over the email list and the lines in the CSV. I was hoping to do this usings Python's maps() function rather than an explicit for loop. The issue is that the object I am iterating over is not indexing the thing I am appending, so I am not sure how to implement that.

Can anyone give some simple tips for how to make the loops faster here?

Answer 1

You dont need two for loops. You need only one, and that is to iterate over the csv for usage data. And then check if line[0] ie user is already present in the dictionary main_data . And then insert to main_data .

for line in read_csv:
    if line[0] in main_data:
        main_data[line[0]].append(line[1])
        main_data[line[0]].append(line[2])