How to write in separate cells with python csvwriter?

I'm reading a sequence of files and writing them and their parameters in lists, then I want to create a csv which looks like this:

What I get with my code:

How can I get each parameter in its own cell? Any help appreciated. What's interesting, if I run the code with just 1 file - parameters put in separate cells.

import csv

files = ['f1', 'f2']
params_a = ['a1', 'a2']
params_p = ['p1', 'p2', 'p3']

with open ('csv.csv', 'a') as csvfile:
        csvwriter = csv.writer(csvfile, delimiter = ',')
        for file in files:
            csvfile.write('\n%s\t' % (file) )
            for parameter_a in params_a:
                csvfile.write('%s\t' % (parameter_a))
            for parameter_p in params_p:
                csvfile.write('%s\t' % (parameter_p))

I tried playing with delemeter, other arguments and line endings but it got worse. Not sure what breaks the 'style' for multiple writing operations.

UPD: updated the table to match the code sample

The most straightforward answer based on the code you provided is this:

files = ["f1", "f2"]
params_a = ["a1", "a2"]
params_p = ["p1", "p2", "p3"]

with open("output_manual.csv", "a", newline="") as csvfile:
    csvwriter = csv.writer(csvfile)

    row = [files[0]] + params_a
    csvwriter.writerow(row)

    row = [files[1]] + params_p
    csvwriter.writerow(row)

That outputs:

f1,a1,a2
f2,p1,p2,p3

That params_a belongs to file "f1", and params_p to "f2", seems to be special knowledge you need to manually code.

If your data actually looked like this:

files = [
    "f1",
    "f2",
]

params = [
    ["a1", "a2"],
    ["p1", "p2", "p3"],
]

Then you can do something like this:

with open("output_mine.csv", "w", newline="") as f_out:
    writer = csv.writer(f_out)
    
    for i, file in enumerate(files):
        row = [file] + params[i]
        writer.writerow(row)

You can also dynmaically size a header, if you like:

max_param_len = 0
for param in params:
    if len(param) > max_param_len:
        max_param_len = len(param)

header = ["File"]
for i in range(max_param_len):
    header += [f"Param_{i+1}"]

and then insert it:

...
writer = csv.writer(f_out)
writer.writerow(header)
...

That outputs:

File,Param_1,Param_2,Param_3
f1,a1,a2
f2,p1,p2,p3

Your data could also look like this and something similar will work:

file_param_map = {
    "f1": ["a1", "a2"],
    "f2": ["p1", "p2", "p3"],
}