We Keep Coding

I did it by the tutorial and it's not working

I found some projects on youtube, and this is one of them.
I'm trying with the password manager program. Here's the link: https://www.youtube.com/watch?v=DLn3jOsNRVE
And here's my code:
from cryptography.fernet import Fernet
'''
def write_key():
key = Fernet.generate_key()
with open("key.key", "wb") as key_file:
key_file.write(key)'''
def load_key():
file = open("key.key", "rb")
key = file.read()
file.close()
return key
key = load_key()
fer = Fernet(key)
def view():
with open('passwords.txt', 'r') as f:
for line in f.readlines():
data = line.rstrip()
user, passw = data.split("|")
print("User:", user, "| Password:",
fer.decrypt(passw.encode()).decode())
def add():
name = input('Account Name: ')
pwd = input("Password: ")
with open('passwords.txt', 'a') as f:
f.write(name + "|" + fer.encrypt(pwd.encode()).decode() + "\n")
while True:
mode = input(
"Would you like to add a new password or view existing ones (view, add), press q to quit? ").lower()
if mode == "q":
break
if mode == "view":
view()
elif mode == "add":
add()
else:
print("Invalid mode.")
continue
#this is a module that will alow you to encrypt txt-s
# pass is used as a placeholder for future code
# rstrip removes any traling chars
#split will look for the char in the arg and it will split the string there
#a append w write r read r+ read and write
#with w mode, you completely overwrite the file so be careful
#with a mode you can add smthing to the end
I followed the instructions precisely and I have no idea what could cause my problem. When I run it, I get an error message:
The guy even has his version of the code on github. I copy-pasted it and still doesn't work
On the video, does the key.key file generate itself, or not?

The only possible code that could write to the key.key file is both:
commented out; and
not called even if it were not commented out,
So, no, it's not correct to say that "the key.key file generate[s] itself".
Looking over the linked video, the presenter at some point (at 1:29:50, more precisely) had the code call that function to create the file, then removed that call and commented out that function.
Likely cause of your problem is that you made a mistake in the process somewhere(1), and this resulted in the file not being created (or being created somewhere other than where it's expected). Suggest you go back to that point in the video and re-do it.
Or, you could just create the key.key file, containing the content (taken from the video):
Raq7IMZ4QkqK20j7lKT3bxJTgwxeJFYx4ADjTqVKdQY=
That may get you going faster than revisiting the steps that the presenter took.
(1) Re your comment that "[t]he guy even has his version of the code on github", it may be that you thought you could bypass the video and just go straight to the final code. If so, that was a mistake, as the final code expects you to have run the incomplete code in order to generate the key file.
If so, I would consider that a failing of the presenter. It would have been far better to leave the keyfile-creating code in and call it, for example, when you ran the code with python the_code.py --make-key-file.

Python doesn't release file after it is closed

What I need to do is to write some messages on a .txt file, close it and send it to a server. This happens in a infinite loop, so the code should look more or less like this:
from requests_toolbelt.multipart.encoder import MultipartEncoder
num = 0
while True:
num += 1
filename = f"example{num}.txt"
with open(filename, "w") as f:
f.write("Hello")
f.close()
mp_encoder = MultipartEncoder(
fields={
'file': ("file", open(filename, 'rb'), 'text/plain')
}
)
r = requests.post("my_url/save_file", data=mp_encoder, headers=my_headers)
time.sleep(10)
The post works if the file is created manually inside my working directory, but if I try to create it and write on it through code, I receive this response message:
500 - Internal Server Error
System.IO.IOException: Unexpected end of Stream, the content may have already been read by another component.
I don't see the file appearing in the project window of PyCharm...I even used time.sleep(10) because at first, I thought it could be a time-related problem, but I didn't solve the problem. In fact, the file appears in my working directory only when I stop the code, so it seems the file is held by the program even after I explicitly called f.close(): I know the with function should take care of closing files, but it didn't look like that so I tried to add a close() to understand if that was the problem (spoiler: it was not)

I solved the problem by using another file
with open(filename, "r") as firstfile, open("new.txt", "a+") as secondfile:
secondfile.write(firstfile.read())
with open(filename, 'w'):
pass
r = requests.post("my_url/save_file", data=mp_encoder, headers=my_headers)
if r.status_code == requests.codes.ok:
os.remove("new.txt")
else:
print("File not saved")
I make a copy of the file, empty the original file to save space and send the copy to the server (and then delete the copy). Looks like the problem was that the original file was held open by the Python logging module

Firstly, can you change open(f, 'rb') to open("example.txt", 'rb'). In open, you should be passing file name not a closed file pointer.
Also, you can use os.path.abspath to show the location to know where file is written.
import os
os.path.abspath('.')
Third point, when you are using with context manager to open a file, you don't close the file. The context manger supposed to do it.
with open("example.txt", "w") as f:
f.write("Hello")

How do I stop new data from python replacing old data in a csv file? [duplicate]

The code below is what I have so far. When it writes to the .csv it overwrites what I had previously written in the file.How can I write to the file in such a way that it doesn't erase my previous text.(The objective of my code is to have a person enter their name and have the program remember them)
def main(src):
try:
input_file = open(src, "r")
except IOError as error:
print("Error: Cannot open '" + src + "' for processing.")
print("Welcome to Learner!")
print("What is your name? ")
name = input()
for line in input_file:
w = line.split(",")
for x in w:
if x.lower() == name.lower():
print("I remember you "+ name.upper())
else:
print("NO")
a = open("learner.csv", "w")
a.write(name)
a.close()
break
if __name__ == "__main__":
main("learner.csv")

You need to append to file the next time. This can be done by opening the file in append mode.
def addToFile(file, what):
f = open(file, 'a').write(what)

change open("learner.csv", "w") to open("learner.csv", "a")
The second parameter with open is the mode, w is write, a is append. With append it automatically seeks to the end of the file.

You'll want to open the file in append-mode ('a'), rathen than write-mode ('w'); the Python documentation explains the different modes available.
Also, you might want to consider using the with keyword:
It is good practice to use the with keyword when dealing with file objects. This has the advantage that the file is properly closed after its suite finishes, even if an exception is raised on the way.
>>> with open('/tmp/workfile', 'a') as f:
... f.write(your_input)

Python read from a file, and only do work if a string isn't found

So I'm trying to make a reddit bot that will exec code from a submission. I have my own sub for controlling these clients.
while __name__ == '__main__':
string = open('config.txt').read()
for submission in subreddit.get_new(limit = 1):
if submission.url not in string:
f.write(submission.url + "\n")
f.close()
f = open('config.txt', "a")
string = open('config.txt').read()
So what this is suppose to do is read from the config file, then only do work if the submission url isn't in config.txt. However, it always sees the most recent post and does it's work. This is how F is opened.
if not os.path.exists('file'):
open('config.txt', 'w').close()
f = open('config.txt', "a")

First a critique of your existing code (in comments):
# the next two lines are not needed; open('config.txt', "a")
# will create the file if it doesn't exist.
if not os.path.exists('file'):
open('config.txt', 'w').close()
f = open('config.txt', "a")
# this is an unusual condition which will confuse readers
while __name__ == '__main__':
# the next line will open a file handle and never explicitly close it
# (it will probably get closed automatically when it goes out of scope,
# but it's not good form)
string = open('config.txt').read()
for submission in subreddit.get_new(limit = 1):
# the next line should check for a full-line match; as written, it
# will match "http://www.test.com" if "http://www.test.com/level2"
# is in config.txt
if submission.url not in string:
f.write(submission.url + "\n")
# the next two lines could be replaced with f.flush()
f.close()
f = open('config.txt', "a")
# this is a cumbersome way to keep your string synced with the file,
# and it never explicitly releases the new file handle
string = open('config.txt').read()
# If subreddit.get_new() doesn't return any results, this will act as
# a busy loop, repeatedly requesting new results as fast as possible.
# If that is undesirable, you might want to sleep here.
# file handle f should get closed after the loop
None of the problems pointed out above should keep your code from working (except maybe the imprecise matching). But simpler code may be easier to debug. Here's some code that does the same thing. Note: I assume there is no chance any other process is writing to config.txt at the same time. You could try this code (or your code) with pdb, line-by-line, to see whether it works as expected.
import time
import praw
r = praw.Reddit(...)
subreddit = r.get_subreddit(...)
if __name__ == '__main__':
# open config.txt for reading and writing without truncating.
# moves pointer to end of file; closes file at end of block
with open('config.txt', "a+") as f:
# move pointer to start of file
f.seek(0)
# make a list of existing lines; also move pointer to end of file
lines = set(f.read().splitlines())
while True:
got_one = False
for submission in subreddit.get_new(limit=1):
got_one = True
if submission.url not in lines:
lines.add(submission.url)
f.write(submission.url + "\n")
# write data to disk immediately
f.flush()
...
if not got_one:
# wait a little while before trying again
time.sleep(10)

python: read file continuously, even after it has been logrotated

I have a simple python script, where I read logfile continuosly (same as tail -f)
while True:
line = f.readline()
if line:
print line,
else:
time.sleep(0.1)
How can I make sure that I can still read the logfile, after it has been rotated by logrotate?
i.e. I need to do the same what tail -F would do.
I am using python 2.7

As long as you only plan to do this on Unix, the most robust way is probably to check so that the open file still refers to the same i-node as the name, and reopen it when that is no longer the case. You can get the i-number of the file from os.stat and os.fstat, in the st_ino field.
It could look like this:
import os, sys, time
name = "logfile"
current = open(name, "r")
curino = os.fstat(current.fileno()).st_ino
while True:
while True:
buf = current.read(1024)
if buf == "":
break
sys.stdout.write(buf)
try:
if os.stat(name).st_ino != curino:
new = open(name, "r")
current.close()
current = new
curino = os.fstat(current.fileno()).st_ino
continue
except IOError:
pass
time.sleep(1)
I doubt this works on Windows, but since you're speaking in terms of tail, I'm guessing that's not a problem. :)

You can do it by keeping track of where you are in the file and reopening it when you want to read. When the log file rotates, you notice that the file is smaller and since you reopen, you handle any unlinking too.
import time
cur = 0
while True:
try:
with open('myfile') as f:
f.seek(0,2)
if f.tell() < cur:
f.seek(0,0)
else:
f.seek(cur,0)
for line in f:
print line.strip()
cur = f.tell()
except IOError, e:
pass
time.sleep(1)
This example hides errors like file not found because I'm not sure of logrotate details such as small periods of time where the file is not available.
NOTE: In python 3, things are different. A regular open translates bytes to str and the interim buffer used for that conversion means that seek and tell don't operate properly (except when seeking to 0 or the end of file). Instead, open in binary mode ("rb") and do the decode manually line by line. You'll have to know the file encoding and what that encoding's newline looks like. For utf-8, its b"\n" (one of the reasons utf-8 is superior to utf-16, btw).

Thanks to #tdelaney and #Dolda2000's answers, I ended up with what follows. It should work on both Linux and Windows, and also handle logrotate's copytruncate or create options (respectively copy then truncate size to 0 and move then recreate file).
file_name = 'my_log_file'
seek_end = True
while True: # handle moved/truncated files by allowing to reopen
with open(file_name) as f:
if seek_end: # reopened files must not seek end
f.seek(0, 2)
while True: # line reading loop
line = f.readline()
if not line:
try:
if f.tell() > os.path.getsize(file_name):
# rotation occurred (copytruncate/create)
f.close()
seek_end = False
break
except FileNotFoundError:
# rotation occurred but new file still not created
pass # wait 1 second and retry
time.sleep(1)
do_stuff_with(line)
A limitation when using copytruncate option is that if lines are appended to the file while time-sleeping, and rotation occurs before wake-up, the last lines will be "lost" (they will still be in the now "old" log file, but I cannot see a decent way to "follow" that file to finish reading it). This limitation is not relevant with "move and create" create option because f descriptor will still point to the renamed file and therefore last lines will be read before the descriptor is closed and opened again.

Using 'tail -F
man tail
-F same as --follow=name --retr
-f, --follow[={name|descriptor}] output appended data as the file grows;
--retry keep trying to open a file if it is inaccessible
-F option will follow the name of the file not descriptor.
So when logrotate happens, it will follow the new file.
import subprocess
def tail(filename: str) -> Generator[str, None, None]:
proc = subprocess.Popen(["tail", "-F", filename], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
while True:
line = proc.stdout.readline()
if line:
yield line.decode("utf-8")
else:
break
for line in tail("/config/logs/openssh/current"):
print(line.strip())

I made a variation of the awesome above one by #pawamoy into a generator function one for my log monitoring and following needs.
def tail_file(file):
"""generator function that yields new lines in a file
:param file:File Path as a string
:type file: str
:rtype: collections.Iterable
"""
seek_end = True
while True: # handle moved/truncated files by allowing to reopen
with open(file) as f:
if seek_end: # reopened files must not seek end
f.seek(0, 2)
while True: # line reading loop
line = f.readline()
if not line:
try:
if f.tell() > os.path.getsize(file):
# rotation occurred (copytruncate/create)
f.close()
seek_end = False
break
except FileNotFoundError:
# rotation occurred but new file still not created
pass # wait 1 second and retry
time.sleep(1)
yield line
Which can be easily used like the below
import os, time
access_logfile = '/var/log/syslog'
loglines = tail_file(access_logfile)
for line in loglines:
print(line)