在新行 Python 中转储（泡菜）

Question

So i want to write each element of a list in a new line in a binary file using Pickle, i want to be able to access these dictionaries later as well.

import pickle    
with open(r'student.dat','w+b') as file: 
for i in [{1:11},{2:22},{3:33},{4:44}]:
    pickle.dump(i,file)
file.seek(0)
print(pickle.load(file))

Output:

{1: 11}

Could someone explain why the rest of the elements arent being dumped or suggest another way to write in a new line? I'm using Python 3

Answer 1

They're all being dumped, but each dump is separate; to load them all, you need to match them with load calls.

import pickle    
with open(r'student.dat','w+b') as file: 
    for i in [{1:11},{2:22},{3:33},{4:44}]:
        pickle.dump(i,file)
file.seek(0)
print(pickle.load(file))


import pickle    
with open(r'student.dat','w+b') as file: 
    for i in [{1:11},{2:22},{3:33},{4:44}]:
        pickle.dump(i,file)
file.seek(0)
for _ in range(4):
    print(pickle.load(file))

If you don't want to perform multiple loads, pickle them as a single data structure (eg the original list of dict s all at once).

In none of these cases are you writing newlines, nor should you be; pickle is a binary protocol, which means newlines are just another byte with independent meaning, and trying to inject newlines into the stream would get in the way of loading the data, and risk splitting up bits of data (if you actually read a line at a time for loading).