import csv
import os
from pathlib import Path
from os import walk

path = os.path.join(os.path.expanduser('~'), 'Documents')

f = []
for (dirpath, dirnames, filenames) in walk(path):
    f.extend(filenames)
    break
inputs = next(walk("~//Documents"), (None, None, []))[2]
# inputs = ["in1.csv", "in2.csv"]  # etc
print(str(len(f))+" files found in "+ path)
print(Path.cwd())

# First determine the field names from the top line of each input file
# Comment 1 below
fieldnames = []
for filename in f:
  with open(os.path.join(path,filename), "r", newline="") as f_in:
    reader = csv.reader(f_in)
    headers = next(reader)
    for h in headers:
      if h not in fieldnames:
        fieldnames.append(h)
print(fieldnames)
# Then copy the data
with open("out.csv", "w", newline="") as f_out:   # Comment 2 below
  writer = csv.DictWriter(f_out, fieldnames=fieldnames)
      writer.writeheader()

  for filename in f:
    with open(os.path.join(path,filename), "r", newline="") as f_in:
      reader = csv.DictReader(f_in)  # Uses the field names in this file
      for line in reader:
        # Comment 3 below
        writer.writerow(line)