有谁知道为什么无法写入.txt文件？

Question

When I run this code and input values for crop and quantity it doesn't write them to crop database.txt like it should, but just creates crop database.txt as a new blank text file. Does anyone know why this is? Is it because of the way I am closing the file?

crop = input("Which crop? ")
quantity = input("How many? ")

with open ('cropdatabase.txt', 'a+') as file:

 lines = file.readlines()

file.close ()

with open ('cropdatabase.txt', 'a+') as file:

 for row in lines:

    if crop in row:

       row = str(a)
       split_2 = a.split (',')
       split_2.append (quantity)

    else:

       file.write ('\n')
       file.write (crop + ' ')
       file.write (quantity + ' ')

file.close ()

Answer 1

If you start with an empty file (or non-existing) the list lines will be empty. So your code for writing anything never runs.

Answer 2

First you need to use raw_input

crop = raw_input("Which crop? ")
quantity = raw_input("How many? ")

Then you do not need f.close() because you have with open.

Answer 3

Hahaha small bug.

• use open(filename, 'r') for reading a file
• use open(filename, 'a') for appending some data to a exsisting file
• use open(filename, 'w') for creating/re-writing a file.

when you open a file with appending 'a', state the file pointer is placed just before EOF(end of file) pointer. So you wont be reading any data.

I would prefer nt using 'a+', it looks great but using a specific format gives more clarity for reading code.

try this

with open ('cropdatabase.txt', 'r') as file:

   lines = file.readlines()

Hope this helps.

Answer 4

Here is your code with comments:

crop = input("Which crop? ")
quantity = input("How many? ")

If you are using python 2, this is a bad idea. use raw_input

with open ('cropdatabase.txt', 'a+') as file:

You are opening this file to append, but are just reading it

 lines = file.readlines()

file.close ()

You don't need to close since you used 'with open'

with open ('cropdatabase.txt', 'a+') as file:

Once again you open to append. You should rewrite the file with 'w'

 for row in lines:

    if crop in row:

       row = str(a)
       split_2 = a.split (',')
       split_2.append (quantity)

This makes no sense to me. What is a?
After mucking with split2 (again, why) you never write anything

    else:

       file.write ('\n')
       file.write (crop + ' ')
       file.write (quantity + ' ')

Now you write crop and quantity to lines that don't have a match?

file.close ()

again, unnecessary close

here is my code

crop = raw_input("Which crop? ")
quantity = raw_input("How many? ")

using raw_input, both will be strings

with open ('cropdatabase.txt', 'r') as file:
    lines = file.readlines()

Read the complete file into lines, then close it (automatically)

with open ('cropdatabase.txt', 'w') as file:
    for row in lines:
        if crop in row:
            row = row.strip(), ", ", quantity
            file.write(row)

You don't specify, so I am writing the row that matches crop and adding the quantity after a comma

        else:
            file.write(row)

Try this and come back with what you see. First save your input file to another name so you can compare the two