pickle — 对象序列化

字符串数据编码和解码

# pickle_string.py
import pickle
import pprint

data = [{'a': 'A', 'b': 2, 'c': 3.0}]
print('DATA:', end=' ')
pprint.pprint(data)

data_string = pickle.dumps(data)
print('PICKLE: {!r}'.format(data_string))

# pickle_unpickle.py
import pickle
import pprint

data1 = [{'a': 'A', 'b': 2, 'c': 3.0}]
print('BEFORE: ', end=' ')
pprint.pprint(data1)

data1_string = pickle.dumps(data1)

data2 = pickle.loads(data1_string)
print('AFTER : ', end=' ')
pprint.pprint(data2)

print('SAME? :', (data1 is data2))
print('EQUAL?:', (data1 == data2))

处理流

# pickle_stream.py
import io
import pickle
import pprint


class SimpleObject:

    def __init__(self, name):
        self.name = name
        self.name_backwards = name[::-1]
        return


data = []
data.append(SimpleObject('pickle'))
data.append(SimpleObject('preserve'))
data.append(SimpleObject('last'))

# Simulate a file.
out_s = io.BytesIO()

# Write to the stream
for o in data:
    print('WRITING : {} ({})'.format(o.name, o.name_backwards))
    pickle.dump(o, out_s)
    out_s.flush()

# Set up a read-able stream
in_s = io.BytesIO(out_s.getvalue())

# Read the data
while True:
    try:
        o = pickle.load(in_s)
    except EOFError:
        break
    else:
        print('READ    : {} ({})'.format(
            o.name, o.name_backwards))

重建对象问题

# pickle_dump_to_file_1.py
import pickle
import sys


class SimpleObject:

    def __init__(self, name):
        self.name = name
        l = list(name)
        l.reverse()
        self.name_backwards = ''.join(l)


if __name__ == '__main__':
    data = []
    data.append(SimpleObject('pickle'))
    data.append(SimpleObject('preserve'))
    data.append(SimpleObject('last'))

    filename = sys.argv[1]

    with open(filename, 'wb') as out_s:
        for o in data:
            print('WRITING: {} ({})'.format(
                o.name, o.name_backwards))
            pickle.dump(o, out_s)

# pickle_load_from_file_1.py
import pickle
import pprint
import sys

filename = sys.argv[1]

with open(filename, 'rb') as in_s:
    while True:
        try:
            o = pickle.load(in_s)
        except EOFError:
            break
        else:
            print('READ: {} ({})'.format(
                o.name, o.name_backwards))

Unpicklable对象

# pickle_state.py
import pickle


class State:

    def __init__(self, name):
        self.name = name

    def __repr__(self):
        return 'State({!r})'.format(self.__dict__)


class MyClass:

    def __init__(self, name):
        print('MyClass.__init__({})'.format(name))
        self._set_name(name)

    def _set_name(self, name):
        self.name = name
        self.computed = name[::-1]

    def __repr__(self):
        return 'MyClass({!r}) (computed={!r})'.format(
            self.name, self.computed)

    def __getstate__(self):
        state = State(self.name)
        print('__getstate__ -> {!r}'.format(state))
        return state

    def __setstate__(self, state):
        print('__setstate__({!r})'.format(state))
        self._set_name(state.name)


inst = MyClass('name here')
print('Before:', inst)

dumped = pickle.dumps(inst)

reloaded = pickle.loads(dumped)
print('After:', reloaded)

循环引用

# pickle_cycle.py
import pickle


class Node:
    """A simple digraph
    """
    def __init__(self, name):
        self.name = name
        self.connections = []

    def add_edge(self, node):
        "Create an edge between this node and the other."
        self.connections.append(node)

    def __iter__(self):
        return iter(self.connections)


def preorder_traversal(root, seen=None, parent=None):
    """Generator function to yield the edges in a graph.
    """
    if seen is None:
        seen = set()
    yield (parent, root)
    if root in seen:
        return
    seen.add(root)
    for node in root:
        recurse = preorder_traversal(node, seen, root)
        for parent, subnode in recurse:
            yield (parent, subnode)


def show_edges(root):
    "Print all the edges in the graph."
    for parent, child in preorder_traversal(root):
        if not parent:
            continue
        print('{:>5} -> {:>2} ({})'.format(
            parent.name, child.name, id(child)))


# Set up the nodes.
root = Node('root')
a = Node('a')
b = Node('b')
c = Node('c')

# Add edges between them.
root.add_edge(a)
root.add_edge(b)
a.add_edge(b)
b.add_edge(a)
b.add_edge(c)
a.add_edge(a)

print('ORIGINAL GRAPH:')
show_edges(root)

# Pickle and unpickle the graph to create
# a new set of nodes.
dumped = pickle.dumps(root)
reloaded = pickle.loads(dumped)

print('\nRELOADED GRAPH:')
show_edges(reloaded)