python_io.md

Data IO (Python functions)

Contents

Data IO (Python functions)

• Data IO (Python Functions)
  • class tf.python_io.TFRecordWriter
  • tf.python_io.tf_record_iterator(path)
  • TFRecords Format Details

Data IO (Python Functions)

A TFRecords file represents a sequence of (binary) strings. The format is not random access, so it is suitable for streaming large amounts of data but not suitable if fast sharding or other non-sequential access is desired.

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class tf.python_io.TFRecordWriter

A class to write records to a TFRecords file.

This class implements __enter__ and __exit__, and can be used in with blocks like a normal file.

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tf.python_io.TFRecordWriter.__init__(path)

Opens file path and creates a TFRecordWriter writing to it.

Args:

• path: The path to the TFRecords file.

Raises:

• IOError: If path cannot be opened for writing.

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tf.python_io.TFRecordWriter.write(record)

Write a string record to the file.

Args:

• record: str

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tf.python_io.TFRecordWriter.close()

Close the file.

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tf.python_io.tf_record_iterator(path)

An iterator that read the records from a TFRecords file.

Args:

• path: The path to the TFRecords file.

Yields:

Strings.

Raises:

• IOError: If path cannot be opened for reading.

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TFRecords Format Details

A TFRecords file contains a sequence of strings with CRC hashes. Each record has the format

uint64 length
uint32 masked_crc32_of_length
byte   data[length]
uint32 masked_crc32_of_data

and the records are concatenated together to produce the file. The CRC32s are described here, and the mask of a CRC is

masked_crc = ((crc >> 15) | (crc << 17)) + 0xa282ead8ul