Python writing int into file

Question

I have a problem with python code and i don't know what to do, because im fairly new in it.

date_now1 = datetime.datetime.now()
archive_date1 = date_now1.strftime("%d.%m.%Y")
f1 = open(archive_date1, "r+")

print("What product do you wish to delete ?")
delate_product = str(input())
for line in f1.readlines():
    if delate_product in line:
        list = line
        ready_product = list.split()
        quantity_of_product = int(ready_product[1])
        if quantity_of_product == 1:
            del line
            print("Product deleted")
        else:
            print("You have {} amounts of this product. How many do you want to delete ?".format(quantity_of_product))
            x = int(input())
            quantity_of_product = quantity_of_product - x
            temporary = "{}".format(quantity_of_product)
            print(type(temporary))
            f1.write(temporary) in ready_product[1]

I get the message

    f1.write(temporary) in ready_product[1] 
TypeError: 'in <string>' requires string as left operand, not int

When i do print(type()) in temporary it says string. I also tried str(quantity_of_product), but it doesn't work as well. Maybe somebody could give me the idea of what to do, or what to read to get the answer.

The error message is correct, as `f1.write(x)` is a function and returns an int. But ... what is that line supposed to do? What it *tries* to do is executing a single statement `a in b`, not even assigning the result to anything. So even if you got rid of that error message, it's still a nonsensical line. — Jongware, Apr 21 '18 at 12:08
What im trying to do is to update quantity in line where the product is in file, after i delete certaint amount of some product. Do so the file would be used as a archive of my grocery shoping — Krystian Dorsz, Apr 21 '18 at 12:19
A file does not support such `a in b` notation – now you explained it, I can see why you thought it *might*. But Python is not an "English parser", it's a regular programming language with preset rules on what syntax you can use when and where. Also, *writing* lines while you are still *reading* from that same file can only end in tears. Read the entire file, make changes, write back. — Jongware, Apr 21 '18 at 12:25

score 2 · Answer 1 · answered Apr 21 '18 at 12:32

The error is arising because you are asking python to find out whether an integer is "in" a string.

The output of f1.write(temporary) is an integer. To see this, try adding a print statement before the erroneous line. In contrast, ready_product[1] is a string (i.e. the second string element in the list "ready_product").

The operator "in" takes two iterables and returns whether the first is "in" the second. For example:

>>> "hello in ["hello", "world"]
>> True
>>> "b" in "a string"
>> False

When Python attempts to see if an integer is "in" a string, it cannot and throws a TypeError, saying "requires string as left operand, not int". This is the root of your error.

You may also have a number of other errors in your code:

"list" is a reserved word in Python, and so calling your variable "list" is bad practice. Try another name such as _list (or delete the variable as it doesn't appear to serve a purpose).
"del line" deletes the variable "line". However, it won't delete the actual line in the text file, only the variable containing it. See Deleting a specific line in a file (python) for how to delete a line from a text file.
There doesn't appear to be a f1.close() statement in the code. This is necessary to close the file after use, as otherwise edits may not be saved.

Personally, instead of attempting to delete lines as I go, I'd maintain a list of lines in the text file, and delete/alter lines from the list as I go. Then, at the end of the program I'd rewrite the file from the list of altered lines.

Python writing int into file

1 Answers1