为什么打印功能在open_with中不起作用？

Question

I am starting a module that opens a file, reads it, does some stuff, and then appends to it. However, I am trying to see what is in the file first. Here is the start of the program:

def addSkill(company):
    with open("companies.txt", "a+") as companies:
        for line in companies:
            print('ok')
            print(line.rstrip('\n'))
        companies.write(company + '\r\n')

    companies.close()

Neither of the print functions are working. There is text in the document. And it appends to it as requested. Any suggestions?

Answer 1

Just open using 'r+' then save in memories everything that you need, then it will automatically writing at the end. because your file descriptor will be at the end.

Opening files in 'a' automatically put your file descriptor at the end, therefore, your can't see what was written before that.

eg

def addSkill(company):
    with open('companies.txt', 'r+') as fd:
        list_of_companies = fd.readlines()
        fd.write(company + '\n')

list_of_companies.append(company) # adding the last company to the full list.
print('\n'.join(list_of_companies)) # print each company with a '\n'.

Bonus : your close() method is useless using with , python will do that for you.

In any cases, when you are unsure about the option of a function, please RTFM : open()

• 'r' open for reading (default)
• 'w' open for writing, truncating the file first
• 'x' open for exclusive creation, failing if the file already exists
• 'a' open for writing, appending to the end of the file if it exists
• 'b' binary mode
• 't' text mode (default)
• '+' open a disk file for updating (reading and writing)
• 'U' universal newlines mode (deprecated)