117 lines
3.9 KiB
Markdown
117 lines
3.9 KiB
Markdown
# [pickle](https://docs.python.org/3/library/pickle.html#module-pickle): Python object serialization
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## The goal
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How to store Python objects in files and how to restore them.
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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**Warning The pickle module is not secure. Only unpickle data you trust.**
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## [pickle](https://docs.python.org/3/library/pickle.html#module-pickle)
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> The [pickle](https://docs.python.org/3/library/pickle.html#module-pickle) module implements binary protocols for serializing and de-serializing a Python object structure. “Pickling” is the process whereby a Python object hierarchy is converted into a byte stream, and “unpickling” is the inverse operation, whereby a byte stream (from a binary file or bytes-like object) is converted back into an object hierarchy.
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## [pickle.dump](https://docs.python.org/3/library/pickle.html#pickle.dump) and [pickle.dumps](https://docs.python.org/3/library/pickle.html#pickle.dumps)
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```python
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pickle.dump(obj, file, protocol=None, *, fix_imports=True, buffer_callback=None)
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```
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> Write the pickled representation of the object obj to the open file object file. This is equivalent to Pickler(file, protocol).dump(obj).
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>
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> Arguments file, protocol, fix_imports and buffer_callback have the same meaning as in the Pickler constructor.
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```python
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pickle.dumps(obj, protocol=None, *, fix_imports=True, buffer_callback=None)
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```
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> Return the pickled representation of the object obj as a bytes object, instead of writing it to a file.
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>
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> Arguments protocol, fix_imports and buffer_callback have the same meaning as in the Pickler constructor.
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```python
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import pickle
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import numpy as np
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class Example:
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a: int
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b: float
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c: np.ndarray
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def __init__(self) -> None:
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super().__init__()
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self.a = 0
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self.b = 0
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self.c = np.zeros((1, 2))
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instance_to_save = Example()
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instance_to_save.a = 1
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instance_to_save.b = 2
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instance_to_save.c[0, 0] = 3
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instance_to_save.c[0, 1] = 4
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with open("test.pkl", "wb") as file:
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pickle.dump(instance_to_save, file)
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print(instance_to_save.a) # -> 1
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print(instance_to_save.b) # -> 2
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print(instance_to_save.c) # -> [[3. 4.]]
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```
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## [pickle.load](https://docs.python.org/3/library/pickle.html#pickle.load) and [pickle.loads](https://docs.python.org/3/library/pickle.html#pickle.loads)
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```python
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pickle.load(file, *, fix_imports=True, encoding='ASCII', errors='strict', buffers=None)
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```
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> Read the pickled representation of an object from the open file object file and return the reconstituted object hierarchy specified therein. This is equivalent to Unpickler(file).load().
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>
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> The protocol version of the pickle is detected automatically, so no protocol argument is needed. Bytes past the pickled representation of the object are ignored.
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>
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> Arguments file, fix_imports, encoding, errors, strict and buffers have the same meaning as in the Unpickler constructor.
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```python
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pickle.loads(data, /, *, fix_imports=True, encoding='ASCII', errors='strict', buffers=None)
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```
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> Return the reconstituted object hierarchy of the pickled representation data of an object. data must be a bytes-like object.
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>
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> The protocol version of the pickle is detected automatically, so no protocol argument is needed. Bytes past the pickled representation of the object are ignored.
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>
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> Arguments fix_imports, encoding, errors, strict and buffers have the same meaning as in the Unpickler constructor.
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```python
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import pickle
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import numpy as np
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class Example:
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a: int
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b: float
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c: np.ndarray
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def __init__(self) -> None:
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super().__init__()
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self.a = 0
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self.b = 0
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self.c = np.zeros((1, 2))
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with open("test.pkl", "rb") as file:
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instance_to_load = pickle.load(file)
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print(instance_to_load.a) # -> 1
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print(instance_to_load.b) # -> 2
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print(instance_to_load.c) # -> [[3. 4.]]
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```
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