# Field Types

## Supported Field Types

: | Field type | Converted to
--- | --- | ---
+ | autoincrement | int
@ | time | datetime.datetime
0 | flags | byte string (int before 2.0)
B | double | float (Visual FoxPro)
B | binary memo | byte string (other versions)
C | text | unicode string
D | date | datetime.date or None
F | float | float
G | OLE object | byte string
I | integer | int
L | logical | True, False or None
M | memo | unicode string (memo), byte string (picture or object) or None
N | numeric | int, float or None
O | double | float (floats are doubles in Python)
P | picture | byte string
T | time | datetime.datetime
V | varchar | unicode string
Y | currency | decimal.Decimal

Text values (‘C’) can be up to 65535 bytes long. DBF was originally limited to 255 bytes but some vendors have reused the `decimal_count` field to get another byte for field length.

The ‘B’ field type is used to store double precision (64 bit) floats in Visual FoxPro databases and binary memos in other versions. `dbfread` will look at the database version to parse and return the correct data type.

The ‘0’ field type is used for ‘_NullFlags’ in Visual FoxPro. It was mistakenly though to always be one byte long and was interpreted as an integer. From 2.0.1 on it is returned as a byte string.

The ‘V’ field is an alternative character field used by Visual FoxPro. The binary version of this field is not yet supported. (See https://msdn.microsoft.com/en-us/library/st4a0s68%28VS.80%29.aspx for more.)

## Adding Custom Field Types

You can add new field types by subclassing `FieldParser`. For example:

    """
    Add custom field parsing by subclassing FieldParser.
    """

    from dbfread import DBF, FieldParser

    class CustomFieldParser(FieldParser):
        def parseC(self, field, data):
            # Return strings reversed.
            return data.rstrip(b' 0').decode()[::-1]

    for record in DBF('files/people.dbf', parserclass=CustomFieldParser):
        print(record['NAME'])

The `FieldParser` object has the following attributes:

self.table

  A reference to the `DBF` objects. This can be used to get the headers to find `dbversion` and other things.

self.encoding

  The character encoding. (A a shortcut for `self.table.encoding` to speed things up a bit.)

self.char_decode_errors

  Error handling scheme to use while decoding. (A shortcut for `self.table.char_decode_errors`.)

self.dbversion

  The database version as an integer. (A shortcut for `self.table.header.dbversion`.)

self.get_memo(index)

  Returns a memo from the memo file using the index stored in the field data.

  This returns a byte string (`bytes`) which you can then decode.

  For Visual FoxPro (`.FPT`) files it will return `TextMemo`, `PictureMemo` and `ObjectMemo` objects depending on the type of memo. These are all subclasses of `bytes` so the type is only used to annotate the memo type without breaking code elsewhere. The full class tree:

      bytes
        VFPMemo
          TextMemo
          BinaryMemo
            PictureMemo
            ObjectMemo

  These are all found in `dbfread.memo`.

self.decode_text(text)

> This will decode the text using the correct encoding and the user supplied `char_decode_errors` option.

## Special Characters in Field Type Names

For a field type like ‘+’ (autoincrement) the method would be named `parse+()`. Since this is not allowed in Python you can instead use its ASCII value in hexadecimal. For example, the ‘+’ parser is called `parse3F()`.

You can name your method with:

    >>> 'parse' + format(ord('?'), 'x').upper()
    'parse3F'

Just replace `'?'` with your field type.

## InvalidValue

The field parser will normally raise `ValueError` when invalid values are encountered. If instead you want them returned as raw data you can do this:

    """
    A field parser that returns invalid values as InvalidValue objects
    instead of raising ValueError.
    """
    from dbfread import DBF, FieldParser, InvalidValue

    class MyFieldParser(FieldParser):
        def parse(self, field, data):
            try:
                return FieldParser.parse(self, field, data)
            except ValueError:
                return InvalidValue(data)

    table = DBF('files/invalid_value.dbf', parserclass=MyFieldParser)
    for i, record in enumerate(table):
        for name, value in record.items():
            if isinstance(value, InvalidValue):
                print('records[{}][{!r}] == {!r}'.format(i, name, value))

`InvalidValue` is a subclass of `bytes`, and allows you to tell invalid data apart from valid data that happens to be byte strings. You can test for this with:

    isinstance(value, InvalidData)

You can also tell from the `repr()` string:

    >>> value
    InvalidData(b'not a number')