dnload/upload with FTP

[ebolisa]

Thank you much! I'm progressing.

This code downloads a file in my directory but, because I'm working with a microprocessor I'd like to download the file into the memories, make changes and upload it again into the ftp server.

How do I go by doing it?
Thank you.

from ftplib import FTP

ftp_server = "192.168.1.10"
url_username = "pi"
url_pass = "mypi"
filepath = "home/pi/iot"
filename = "blynk.json"

ftp = FTP(ftp_server)
print(ftp.login(url_username, url_pass))  # 230 User pi logged in
print(ftp.cwd(filepath))  # 250 CWD command successful
print(ftp.retrlines('LIST'))  # 226 Transfer complete

with open(filename, "wb") as fp:
    # use FTP's RETR command to download the file
    ftp.retrbinary(f"RETR {filename}", fp.write)

print(ftp.quit())  # 221 Goodbye

EDIT:
This' what I tried:

from ftplib import FTP
from io import BytesIO
import json

ftp_server = "192.168.1.10"
url_username = "pi"
url_pass = "mypi"
filepath = "home/pi/iot"
filename = "blynk.json"
data = []

def getFile(ftp, filename):
    try:
        ftp.retrbinary("RETR " + filename, open(filename, 'wb').write)
    except:
        print("Error")

ftp = FTP(ftp_server)
ftp.login(url_username, url_pass)
ftp.cwd(filepath)
data.append(getFile(ftp, filename))
print(data)  # [None]
ftp.quit()

EDIT 2:

from ftplib import FTP
from io import BytesIO
import json


def getFile(fp, fname):
    try:
        r = BytesIO()
        fp.retrbinary("RETR " + fname, r.write)
        data = r.getvalue().decode("utf-8")
        data = json.loads(data)  # convert str to json
        return data
    except:
        print("ftp read error")


def postFile(fp, fname, file):
    try:
        fp.storbinary("STOR" + fname, file)
    except:
        print("ftp post error")

# open ftp connection
ftp = FTP(ftp_server)

# login
ftp.login(url_username, url_pass)  # 230 User pi logged in

# change directory
ftp.cwd(filepath)  # 250 CWD command successful

# list dir
# print(ftp.retrlines('LIST'))  # 226 Transfer complete

# retrieve json data
js_data = getFile(ftp, filename)

print(js_data)

# update json data
js_data["relay3"] = "5555"

print(js_data)  # shows updated data

# upload file
postFile(ftp, filename, js_data)

# close ftp connection
ftp.quit()  # 221 Goodbye

Error:
ftp post error