How to make it so my code remembers what is has written in a text file? - python-3.x

Question

Hello python newbie here.
I have code that prints names into a text file. It takes the names from a website. And on that website, there may be multiple same names. It filters them perfectly without an issue into one name by looking if the name has already written in the text file. But when I run the code again it ignores the names that are already in the text file. It just filters the names it has written on the same session. So my question is how do I make it remember what it has written.
image of the text file
kaupan_nimi = driver.find_element_by_xpath("//span[#class='store_name']").text
with open("mainostetut_yritykset.txt", "r+") as tiedosto:
if kaupan_nimi in tiedosto:
print("\033[33mNimi oli jo tiedostossa\033[0m")
else:
print("\033[32mUusi asiakas vahvistettu!\033[0m")
#Kirjoittaa tekstitiedostoon yrityksen nimen
tiedosto.seek(0)
data = tiedosto.read(100)
if len(data) > 0:
tiedosto.write("\n")
tiedosto.write(kaupan_nimi)
There is the code that I think is the problem. Please correct me if I am wrong.

Answer 1

There are two main issues with your current code.
The first is that you are likely only going to be able to detect duplicated names if they are back to back. That is, if the prior name that you're seeing again was the very last thing written into the file. That's because all the lines in the file except the last one will have newlines at the end of them, but your names do not have newlines. You're currently looking for an exact match for a name as a line, so you'll only ever have a chance to see that with the last line, since it doesn't have a newline yet. If the list of names you are processing is sorted, the duplicates will naturally be clumped together, but if you add in some other list of names later, it probably won't pick up exactly where the last list left off.
The second issue in your code is that it will tend to clobber anything that gets written more than 100 characters into the file, starting every new line at that point, once it starts filling up a bit.
Lets look at the different parts of your code:
if kaupan_nimi in tiedosto:
This is your duplicate check, it treats the file as an iterator and reads each line, checking if kaupan_nimi is an exact match to any of them. This will always fail for most of the lines in the file because they'll end with "\n" while kaupan_nimi does not.
I would suggest instead reading the file only once per batch of names, and keeping a set of names in your program's memory that you can check your names-to-be-added against. This will be more efficient, and won't require repeated reading from the disk, or run into newline issues.
tiedosto.seek(0)
data = tiedosto.read(100)
if len(data) > 0:
tiedosto.write("\n")
This code appears to be checking if the file is empty or not. However, it always leaves the file position just past character 100 (or at the end of the file if there were fewer than 100 characters in it so far). You can probably fit several names in that first 100 characters, but after that, you'll always end up with the names starting at index 100 and going on from there. This means you'll get names written on top of each other.
If you take my earlier advice and keep a set of known names, you could check that set to see if it is empty or not. This doesn't require doing anything to the file, so the position you're operating on it can remain at the end all of the time. Another option is to always end every line in the file with a newline so that you don't need to worry about whether to prepend a newline only if the file isn't empty, since you know that at the end of the file you'll always be writing a fresh line. Just follow each name with a newline and you'll always be doing the right thing.
Here's how I'd put things together:
# if possible, do this only once, at the start of the website reading procedure:
with open("mainostetut_yritykset.txt", "r+") as tiedosto:
known_names = set(name.strip() for name in tiedosto) # names already in the file
# do the next parts in some kind of loop over the names you want to add
for name in something():
if name in known_names: # duplicate found
print("\033[33mNimi oli jo tiedostossa\033[0m")
else: # not a duplicate
print("\033[32mUusi asiakas vahvistettu!\033[0m")
tiedosto.write(kaupan_nimi) # write out the name
tiedosto.write("\n") # and always add a newline afterwards
# alternatively, if you can't have a trailing newline at the end, use:
# if known_names:
# tiedosto.write("\n")
# tiedosto.write(kaupan_nimi)
known_names.add(kaupan_nimi) # update the set of names