一 pickle
pickle模塊用來實現python對象的序列化和反序列化。通常地pickle將python對象序列化為二進制流或文件。
python對象與文件之間的序列化和反序列化：
pickle.dump()
pickle.load()
如果要實現python對象和字符串間的序列化和反序列化，則使用：
pickle.dumps()
pickle.loads()
可以被序列化的類型有：
* None,True 和 False;
* 整數，浮點數，復數;
* 字符串，字節流，字節數組;
* 包含可pickle對象的tuples，lists，sets和dictionaries；
* 定義在module頂層的函數：
* 定義在module頂層的內置函數；
* 定義在module頂層的類；
* 擁有__dict__()或__setstate__()的自定義類型；
注意：對於函數或類的序列化是以名字來識別的，所以需要import相應的module。
二 pickle的運行過程
在大部分情況下，要是的對象picklable，我們不需要額外的代碼。默認地pickle將智能地檢查類和實例的屬性，當一個類實例反序列化的時候，它的__init__()方法通常不被調用。而是首先創建一個未初始化的實例，然后再回復存儲的屬性。
但是可以通過實現下列的方法來修改默認的行為：
object.__getstate__() :默認地序列化對象的__dict__,但是如果你實現了__getstate__(),則__getstate__()函數返回的值將被序列化。
object.__setstate__(state) :如果類型實現了此方法，則在反序列化的時候，此方法用來恢復對象的屬性。
object.__getnewargs__() ： 如果實例構造的時候（__new__()）需要參數，則需要實現此函數。
注意：如果__getstate__()返回False，則在反序列化的時候__setstate__()則不被調用。
有的時候為了效率，或上面的3個函數不能滿足需求時，需要實現__reduce__()函數。
三 實例
import pickle
# An arbitrary collection of objects supported by pickle.
data = {
' a ': [1, 2.0, 3, 4+6j],
' b ': ( " character string ", b " byte string "),
' c ': set([None, True, False])
}
with open( ' data.pickle ', ' wb ') as f:
# Pickle the 'data' dictionary using the highest protocol available.
pickle.dump(data, f, pickle.HIGHEST_PROTOCOL)
with open( ' data.pickle ', ' rb ') as f:
# The protocol version used is detected automatically, so we do not
# have to specify it.
data = pickle.load(f)
print(str(data))
# An arbitrary collection of objects supported by pickle.
data = {
' a ': [1, 2.0, 3, 4+6j],
' b ': ( " character string ", b " byte string "),
' c ': set([None, True, False])
}
with open( ' data.pickle ', ' wb ') as f:
# Pickle the 'data' dictionary using the highest protocol available.
pickle.dump(data, f, pickle.HIGHEST_PROTOCOL)
with open( ' data.pickle ', ' rb ') as f:
# The protocol version used is detected automatically, so we do not
# have to specify it.
data = pickle.load(f)
print(str(data))
四 修改picklable類型的默認行為
class TextReader:
""" Print and number lines in a text file. """
def __init__(self, filename):
self.filename = filename
self.file = open(filename)
self.lineno = 0
def readline(self):
self.lineno += 1
line = self.file.readline()
if not line:
return None
if line.endswith( ' \n '):
line = line[:-1]
return " %i: %s " % (self.lineno, line)
def __getstate__(self):
# Copy the object's state from self.__dict__ which contains
# all our instance attributes. Always use the dict.copy()
# method to avoid modifying the original state.
state = self. __dict__.copy()
# Remove the unpicklable entries.
del state[ ' file ']
return state
def __setstate__(self, state):
# Restore instance attributes (i.e., filename and lineno).
self. __dict__.update(state)
# Restore the previously opened file's state. To do so, we need to
# reopen it and read from it until the line count is restored.
file = open(self.filename)
for _ in range(self.lineno):
file.readline()
# Finally, save the file.
self.file = file
reader = TextReader( " hello.txt ")
print(reader.readline())
print(reader.readline())
s = pickle.dumps(reader)
# print(s)
new_reader = pickle.loads(s)
print(new_reader.readline())
# the output is
# 1: hello
# 2: how are you
# 3: goodbye
""" Print and number lines in a text file. """
def __init__(self, filename):
self.filename = filename
self.file = open(filename)
self.lineno = 0
def readline(self):
self.lineno += 1
line = self.file.readline()
if not line:
return None
if line.endswith( ' \n '):
line = line[:-1]
return " %i: %s " % (self.lineno, line)
def __getstate__(self):
# Copy the object's state from self.__dict__ which contains
# all our instance attributes. Always use the dict.copy()
# method to avoid modifying the original state.
state = self. __dict__.copy()
# Remove the unpicklable entries.
del state[ ' file ']
return state
def __setstate__(self, state):
# Restore instance attributes (i.e., filename and lineno).
self. __dict__.update(state)
# Restore the previously opened file's state. To do so, we need to
# reopen it and read from it until the line count is restored.
file = open(self.filename)
for _ in range(self.lineno):
file.readline()
# Finally, save the file.
self.file = file
reader = TextReader( " hello.txt ")
print(reader.readline())
print(reader.readline())
s = pickle.dumps(reader)
# print(s)
new_reader = pickle.loads(s)
print(new_reader.readline())
# the output is
# 1: hello
# 2: how are you
# 3: goodbye
完！