读/写文件：“a”比“a+”模式快吗？

Question

Based on many people's answer, it looks the only difference between "a" and "a+" mode is that "a+" is not only write/append, but also "read".

From my using file open experience, without "a+" mode, I can do write append with "a" pretty well. Does "a" give me performance improvement if I don't need read for the file at all?

For example:

with open('file.txt', 'a') as f:
    f.write('line\n');

Answer 1

If you run this test on identical text files, the loop using 'a+' runs about one one hundredth of a second slower that 'a'. This difference does not change significantly as the test is repeated and the files continue to grow larger and larger. This would indicate that even though 'a+' is very slightly slower, it does not seem to spend any extra time reading the file first.

from time import time

start = time ()
with open ('testfile1.txt', 'a') as file :
    for index in range (9999) :
        file.write ('This is a test to see how long this will take.\n')
stop = time ()
first_total = stop - start

start = time ()
with open ('testfile2.txt', 'a+') as file :
    for index in range (9999) :
        file.write ('This is a test to see how long this will take.\n')
stop = time ()
second_total = stop - start

print ('First = ', first_total)
print ('Second = ', second_total)
print ('Differenct = ', second_total - first_total)