pickle के साथ Binary Files

import pickle
pickle.dump(object, file_object)     # file opened in 'wb' or 'ab'
object = pickle.load(file_object)    # file opened in 'rb'

import pickle
data = {'roll': 1, 'name': 'Asha', 'marks': 91.5}
with open('one.dat', 'wb') as f:          # 'wb' = write binary
    pickle.dump(data, f)                  # serialise (pickle) the object
with open('one.dat', 'rb') as f:          # 'rb' = read binary
    back = pickle.load(f)                 # deserialise (unpickle)
print(back, type(back))

import pickle
def write_records():
    students = [[1, 'Asha', 91.5], [2, 'Ravi', 72.0], [3, 'Neha', 85.0], [4, 'Kabir', 64.5]]
    with open('student.dat', 'wb') as f:
        for rec in students:
            pickle.dump(rec, f)           # one dump per record
    print(len(students), 'records written')
write_records()

import pickle
def read_all():
    with open('student.dat', 'rb') as f:
        while True:
            try:
                rec = pickle.load(f)
                print(rec)
            except EOFError:              # end of file reached
                break
read_all()

import pickle
def search(roll):
    found = False
    with open('student.dat', 'rb') as f:
        try:
            while True:
                rec = pickle.load(f)
                if rec[0] == roll:
                    print('Found:', rec)
                    found = True
        except EOFError:
            pass
    if not found:
        print('Roll', roll, 'not found')
search(3)
search(9)

import pickle
def count_above(limit):
    n = 0
    with open('student.dat', 'rb') as f:
        try:
            while True:
                if pickle.load(f)[2] > limit:
                    n += 1
        except EOFError:
            pass
    return n
print('Students above 80:', count_above(80))

import pickle
def append_record(rec):
    with open('student.dat', 'ab') as f:   # 'ab' keeps old records
        pickle.dump(rec, f)
append_record([5, 'Meher', 88.0])
with open('student.dat', 'rb') as f:
    recs = []
    try:
        while True:
            recs.append(pickle.load(f))
    except EOFError:
        pass
print(len(recs), 'records; last =', recs[-1])

import pickle
def update_marks(roll, new_marks):
    recs = []
    with open('student.dat', 'rb') as f:          # 1. read all records
        try:
            while True:
                recs.append(pickle.load(f))
        except EOFError:
            pass
    for r in recs:                                # 2. change in memory
        if r[0] == roll:
            r[2] = new_marks
    with open('student.dat', 'wb') as f:          # 3. write all back
        for r in recs:
            pickle.dump(r, f)
update_marks(2, 78.0)
with open('student.dat', 'rb') as f:
    pickle.load(f)
    print(pickle.load(f))                         # second record

import pickle
def delete_record(roll):
    keep = []
    with open('student.dat', 'rb') as f:
        try:
            while True:
                r = pickle.load(f)
                if r[0] != roll:
                    keep.append(r)
        except EOFError:
            pass
    with open('student.dat', 'wb') as f:
        for r in keep:
            pickle.dump(r, f)
    print('Remaining rolls:', [r[0] for r in keep])
delete_record(4)

import pickle
# A whole list or dictionary can also be dumped in ONE go
book = {'B1': ('Python', 450), 'B2': ('SQL', 380)}
with open('books.dat', 'wb') as f:
    pickle.dump(book, f)
with open('books.dat', 'rb') as f:
    b = pickle.load(f)
for code, (title, price) in b.items():
    print(code, title, price)

import pickle
with open('student.dat', 'rb') as f:
    pickle.load(f)
    pos = f.tell()                # byte position after the first record
    second = pickle.load(f)
    f.seek(pos)                   # go back and read the same record again
    print(second == pickle.load(f), pos > 0)