A PKL file stores serialized Python objects created with the pickle module. Pickling converts a Python object into a byte stream for writing to disk. Unpickling reverses this to deserialize the byte stream back into a Python object. PKL files enable efficient storage and transfer of Python objects.
The pickle module is part of the Python standard library. To create a PKL file in Python: import pickle, open a file for writing bytes, and use pickle.dump() to serialize the object. To read a PKL file: open the file for reading bytes and use pickle.load() to deserialize into a Python object.
PKL files belong to the broader category of serialized object formats. Such formats allow complex object hierarchies to be saved efficiently. Along with pickle, other examples include JSON, Protocol Buffers, Apache Avro, and Apache Thrift. Programs in any language can use these formats to serialize objects for storage and transmission.
While mainly associated with Python pickle, PKL files also relate to Microsoft Exchange Server migration. The Exchange Migration Wizard uses PKL files when migrating data between Exchange servers. So PKL files may contain migrated Exchange data rather than pickled Python objects.