Python 2.7-在文本文件的列表中添加和删除项目

Question

For example I have a text file with a list.

What I want to do.

Read the text file and find the list. Add/remove an item from the list. Write the amended list back to the text file or at least a new version of the text file.

I can do this in memory as shown below. But want to open a file, edit the list and then write to disk. I'm new to Python, so some code examples would be great.

myfile = “/users/admin/desktop/list.txt”
mylist = ["red", "blue", "green", "yellow", "white"]
myitem = "orange"

with open(myfile) as f:
    mylist = list(f)
    mylist.append(myitem)  


with open(myfile) as f:
    mylist = list(f)
    mylist.remove(myitem)

Answer 1

Nothing fancy, just a simple replace all of the text in the file with contents of the new file, use eval() to convert text to a list. You should probably create a function that writes list to the file and call it after you change the list:

print(mylist)
print(open(myfile).read())

with open(myfile) as f:
    mylist = eval(f.read())
    mylist.append(myitem)

with open(myfile, 'w') as f:
    f.write(str(mylist))

print(mylist)
print(open(myfile).read())

with open(myfile) as f:
    mylist = eval(f.read())
    mylist.remove(myitem)

with open(myfile, 'w') as f:
    f.write(str(mylist))

print(mylist)
print(open(myfile).read())

Output:

['red', 'blue', 'green', 'yellow', 'white']
["red", "blue", "green", "yellow", "white"]
['red', 'blue', 'green', 'yellow', 'white', 'orange']
['red', 'blue', 'green', 'yellow', 'white', 'orange']
['red', 'blue', 'green', 'yellow', 'white']
['red', 'blue', 'green', 'yellow', 'white']

Answer 2

If the point of the file is simply to have persistent storage of the list, have you considered just using pickle? https://docs.python.org/2/library/pickle.html

Answer 3

If it truly is comma seperated, I'd use the csv module ( docs ). It's fairly straightforward.

import csv

with open(myfile) as rfp, open(myfile + '.v2', 'w') as wfp:
    reader = csv.reader(rfp)
    writer = csv.writer(wfp)
    for row in reader:
        row.append(myitem)
        # do something here I suppose
        row.remove(myitem)
        writer.writerow(row)

You may have to use the docs to adjust the reader and writer settings to your operating system and/or file format but I've had great success with that module.

Good luck!