### Install pyiso8583

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/index.rst.txt

Command to install the package via pip.

```bash
pip install pyiso8583
```

--------------------------------

### Define ASCII field configurations

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configuration dictionary entries for ISO 8583 fields using ASCII encoding.

```json
"124": {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 999, "desc": "Reserved for Private Use"},
"125": {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 999, "desc": "Reserved for Private Use"},
"126": {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 999, "desc": "Reserved for Private Use"},
"127": {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 999, "desc": "Reserved for Private Use"},
"128": {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 16,  "desc": "MAC"}
}
```

--------------------------------

### Auto-generate secondary bitmap

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

Demonstrates automatic secondary bitmap generation when a field in the 65-128 range is included.

```python
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> decoded = {
...     't': '0200',
...     '102': '111111'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02008000000000000000000000000400000006111111')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'8000000000000000'},
 '1': {'len': b'', 'data': b'0000000004000000'},
 '102': {'len': b'06', 'data': b'111111'}}
>>> pprint.pp(decoded)
{'t': '0200', '102': '111111', 'p': '8000000000000000', '1': '0000000004000000'}
```

--------------------------------

### iso8583.pp(doc, spec, desc_width=30, stream=None, line_width=80)

Source: https://pyiso8583.readthedocs.io/en/latest/_modules/iso8583/tools.html

Pretty prints a Python dictionary containing ISO8583 data to a specified output stream.

```APIDOC
## iso8583.pp

### Description
Pretty prints a Python dictionary containing ISO8583 data. It is recommended to call this after decoding or encoding data to ensure the most accurate information is displayed.

### Parameters
- **doc** (dict) - Required - The dictionary containing the ISO8583 data.
- **spec** (dict) - Required - A Python dictionary defining the ISO8583 specification.
- **desc_width** (int) - Optional - Field description width (default 30). Specify 0 to print no descriptions.
- **stream** (TextIO) - Optional - An output stream. If not specified, defaults to sys.stdout.
- **line_width** (int) - Optional - The attempted maximum width of the output line (default 80).
```

--------------------------------

### Add and Remove Fields in ISO8583 Messages

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Shows how to add fields by key and remove them using standard dictionary methods before re-encoding.

```python
>>> decoded['2'] = 'cardholder PAN'
>>> decoded['3'] = '111111'
>>> decoded['21'] = '021'
>>>
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'0200600008000000000014cardholder PAN111111021')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'6000080000000000'},
 '2': {'len': b'14', 'data': b'cardholder PAN'},
 '3': {'len': b'', 'data': b'111111'},
 '21': {'len': b'', 'data': b'021'}}
>>> pprint.pp(decoded)
{'t': '0200',
 'p': '6000080000000000',
 '2': 'cardholder PAN',
 '3': '111111',
 '21': '021'}
```

```python
>>> decoded.pop('2', None)
'cardholder PAN'
>>> decoded.pop('3', None)
'111111'
>>>
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02000000080000000000021')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'0000080000000000'},
 '21': {'len': b'', 'data': b'021'}}
>>> pprint.pp(decoded)
{'t': '0200', 'p': '0000080000000000', '21': '021'}
```

--------------------------------

### Default ASCII Field Definitions

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

A comprehensive dictionary mapping ISO 8583 fields to their ASCII encoding specifications.

```json
default_ascii = {
"h":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 0,   "desc": "Message Header"},
"t":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Message Type"},
"p":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 16,  "desc": "Bitmap, Primary"},
"1":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 16,  "desc": "Bitmap, Secondary"},
"2":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 19,  "desc": "Primary Account Number (PAN)"},
"3":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "Processing Code"},
"4":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Transaction"},
"5":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Settlement"},
"6":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Cardholder Billing"},
"7":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 10,  "desc": "Transmission Date and Time"},
"8":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Amount, Cardholder Billing Fee"},
"9":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Conversion Rate, Settlement"},
"10":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Conversion Rate, Cardholder Billing"},
"11":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "System Trace Audit Number"},
"12":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "Time, Local Transaction"},
"13":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Local Transaction"},
"14":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Expiration"},
"15":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Settlement"},
"16":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Conversion"},
"17":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Capture"},
"18":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Merchant Type"},
"19":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Acquiring Institution Country Code"},
"20":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "PAN Country Code"},
"21":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Forwarding Institution Country Code"},
"22":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Point-of-Service Entry Mode"},
"23":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "PAN Sequence Number"},
"24":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Network International ID (NII)"},
"25":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 2,   "desc": "Point-of-Service Condition Code"},
"26":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 2,   "desc": "Point-of-Service Capture Code"},
"27":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 1,   "desc": "Authorizing ID Response Length"},
"28":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Transaction Fee"},
"29":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Settlement Fee"},
"30":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Transaction Processing Fee"},
"31":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Settlement Processing Fee"},
"32":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 11,  "desc": "Acquiring Institution ID Code"},
"33":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 11,  "desc": "Forwarding Institution ID Code"},
"34":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 28,  "desc": "Primary Account Number, Extended"},
"35":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 37,  "desc": "Track 2 Data"},
"36":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 104, "desc": "Track 3 Data"}
}
```

--------------------------------

### Encode a Basic ISO8583 Message

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Demonstrates the minimum requirement of a message type key 't' to encode a dictionary into a bytearray.

```python
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> decoded = {'t': '0200'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02000000000000000000')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'0000000000000000'}}
>>> pprint.pp(decoded)
{'t': '0200', 'p': '0000000000000000'}
```

--------------------------------

### Add fields to an ISO8583 message

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

Shows how to include additional data fields in the message dictionary before re-encoding.

```python
>>> decoded['2'] = 'cardholder PAN'
>>> decoded['3'] = '111111'
>>> decoded['21'] = '021'
>>>
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'0200600008000000000014cardholder PAN111111021')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'6000080000000000'},
 '2': {'len': b'14', 'data': b'cardholder PAN'},
 '3': {'len': b'', 'data': b'111111'},
 '21': {'len': b'', 'data': b'021'}}
>>> pprint.pp(decoded)
{'t': '0200',
 'p': '6000080000000000',
 '2': 'cardholder PAN',
 '3': '111111',
 '21': '021'}
```

--------------------------------

### Send Binary Data

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Configure field specifications dynamically to handle binary data, such as EMV fields, by setting encoding types.

```python
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> decoded = {
...     't': '0200',
...     '55': '9F02060000000123455F340102'}
```

```python
>>> spec['55']['data_enc'] = 'b'
>>> spec['55']['len_enc'] = 'ascii'
>>> spec['55']['len_type'] = 3
>>> spec['55']['max_len'] = 999
```

```python
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02000000000000000200013\x9f\x02\x06\x00\x00\x00\x01#E_4\x01\x02')
```

--------------------------------

### Send Binary Coded Decimal (BCD) Data

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Handle BCD fields by configuring nibble-based length counting and padding for odd-length data.

```python
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> decoded = {
...     't': '0200',
...     '2': '121200000002121'}
```

```python
>>> spec['2']['data_enc'] = 'b'
>>> spec['2']['len_enc'] = 'b'
>>> spec['2']['len_type'] = 1
>>> spec['2']['max_len'] = 19
>>> spec['2']['len_count'] = 'nibbles'
>>> spec['2']['right_pad'] = '0'
```

```python
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02004000000000000000\x15\x12\x12\x00\x00\x00\x02\x12\x10')
```

--------------------------------

### Pad BCD or Hex Fields

Source: https://pyiso8583.readthedocs.io/en/latest/_modules/iso8583/encoder.html

Pads a field from the left or right based on the provided field specification.

```python
def _add_pad_field(
    field_data: str,
    field_spec: _FieldSpecDict,
) -> str:
    r"""Pad a BCD or hex field from the left or right.

    Parameters
    ----------
    doc_dec : dict
        Dict containing decoded ISO8583 data
    field_data : str
        Field data to encode
    field_key : str
        Field ID to pad
    field_spec : dict
        A Python dict defining ISO8583 specification for this field.
        See :mod:`iso8583.specs` module for examples.

    Returns
    -------
    str
        Padded field data
    """
    pad: str = field_spec.get("left_pad", "")[:1]
    if len(pad) > 0:
        return pad + field_data

    pad = field_spec.get("right_pad", "")[:1]
    if len(pad) > 0:
        return field_data + pad

    return field_data
```

--------------------------------

### Define ISO 8583 Message Specification Dictionary

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

A sample dictionary configuration for ISO 8583 message fields, specifying encoding and length constraints for various data elements.

```python
default = {
"h":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 0,   "desc": "Message Header"},
"t":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Message Type"},
"p":   {"data_enc": "b",     "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Bitmap, Primary"},
"1":   {"data_enc": "b",     "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Bitmap, Secondary"},
"2":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 19,  "desc": "Primary Account Number (PAN)"},
"3":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "Processing Code"},
"4":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Transaction"},
"5":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Settlement"},
"6":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Amount, Cardholder Billing"},
"7":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 10,  "desc": "Transmission Date and Time"},
"8":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Amount, Cardholder Billing Fee"},
"9":   {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Conversion Rate, Settlement"},
"10":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 8,   "desc": "Conversion Rate, Cardholder Billing"},
"11":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "System Trace Audit Number"},
"12":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "Time, Local Transaction"},
"13":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Local Transaction"},
"14":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Expiration"},
"15":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Settlement"},
"16":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Conversion"},
"17":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Date, Capture"},
"18":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 4,   "desc": "Merchant Type"},
"19":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Acquiring Institution Country Code"},
"20":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "PAN Country Code"},
"21":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Forwarding Institution Country Code"},
"22":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Point-of-Service Entry Mode"},
"23":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "PAN Sequence Number"},
"24":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 3,   "desc": "Network International ID (NII)"},
"25":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 2,   "desc": "Point-of-Service Condition Code"},
"26":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 2,   "desc": "Point-of-Service Capture Code"},
"27":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 1,   "desc": "Authorizing ID Response Length"},
"28":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Transaction Fee"},
"29":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Settlement Fee"},
"30":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Transaction Processing Fee"},
"31":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 9,   "desc": "Amount, Settlement Processing Fee"},
"32":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 11,  "desc": "Acquiring Institution ID Code"},
"33":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 11,  "desc": "Forwarding Institution ID Code"},
"34":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 28,  "desc": "Primary Account Number, Extended"},
"35":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 2, "max_len": 37,  "desc": "Track 2 Data"},
"36":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 3, "max_len": 104, "desc": "Track 3 Data"},
"37":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 12,  "desc": "Retrieval Reference Number"},
"38":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 6,   "desc": "Authorization ID Response"},
"39":  {"data_enc": "ascii", "len_enc": "ascii", "len_type": 0, "max_len": 2,   "desc": "Response Code"}
```

--------------------------------

### Manage Secondary Bitmaps

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Explains that secondary bitmaps are auto-generated when fields 65-128 are present and that manual bitmap values are overwritten.

```python
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> decoded = {
...     't': '0200',
...     '102': '111111'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02008000000000000000000000000400000006111111')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'8000000000000000'},
 '1': {'len': b'', 'data': b'0000000004000000'},
 '102': {'len': b'06', 'data': b'111111'}}
>>> pprint.pp(decoded)
{'t': '0200', '102': '111111', 'p': '8000000000000000', '1': '0000000004000000'}
```

```python
>>> decoded = {
...     't': '0200',
...     'p': 'spam',
...     '1': 'eggs',
...     '102': '111111'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02008000000000000000000000000400000006111111')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'8000000000000000'},
 '1': {'len': b'', 'data': b'0000000004000000'},
 '102': {'len': b'06', 'data': b'111111'}}
>>> pprint.pp(decoded)
{'t': '0200', 'p': '8000000000000000', '102': '111111', '1': '0000000004000000'}
```

```python
>>> decoded = {
...     't': '0200',
...     'p': 'spam',
...     '1': 'eggs',
...     '21': '051'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02000000080000000000051')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'0000080000000000'},
 '21': {'len': b'', 'data': b'051'}}
>>> pprint.pp(decoded)
{'t': '0200', 'p': '0000080000000000', '21': '051'}
```

--------------------------------

### Pretty print ISO8583 messages

Source: https://pyiso8583.readthedocs.io/en/latest/intro.html

Use iso8583.pp to display decoded or encoded messages in a human-readable format.

```python
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> encoded_raw = b'02004000000000000000101234567890'
>>> decoded, encoded = iso8583.decode(encoded_raw, spec)
>>> iso8583.pp(decoded, spec)
t   Message Type                  : '0200'
p   Bitmap, Primary               : '4000000000000000'
2   Primary Account Number (PAN)  : '1234567890'
>>> iso8583.pp(encoded, spec)
t   Message Type                  : b'0200'
p   Bitmap, Primary               : b'4000000000000000'
2   Primary Account Number (PAN)  : b'10' b'1234567890'
```

--------------------------------

### Convert ISO8583 Data to JSON

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

Serialize decoded ISO8583 message dictionaries into JSON strings using the standard json library.

```python
>>> import json
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> encoded_raw = b'0200600008000000000014cardholder PAN111111021'
>>> decoded, encoded = iso8583.decode(encoded_raw, spec)
>>> pprint.pp(decoded)
{'t': '0200',
 'p': '6000080000000000',
 '2': 'cardholder PAN',
 '3': '111111',
 '21': '021'}
>>> decoded_json = json.dumps(decoded)
>>> decoded_json
'{"t": "0200", "p": "6000080000000000", "2": "cardholder PAN", "3": "111111", "21": "021"}'
```

--------------------------------

### Define DecodeError Exception

Source: https://pyiso8583.readthedocs.io/en/latest/_modules/iso8583/decoder.html

Custom exception class for ISO8583 decoding errors, capturing state information like position and field name.

```python
class DecodeError(ValueError):
    r"""Subclass of ValueError that describes ISO8583 decoding error.

    Attributes
    ----------
    msg : str
        The unformatted error message
    s : bytes or bytearray
        The ISO8583 bytes instance being parsed
    doc_dec : dict
        Dict containing partially decoded ISO8583 data
    doc_enc : dict
        Dict containing partially encoded ISO8583 data
    pos : int
        The start index where ISO8583 bytes data failed parsing
    field : str
        The ISO8583 field where parsing failed
    """

    def __init__(
        self,
        msg: str,
        s: Union[bytes, bytearray],
        doc_dec: DecodedDict,
        doc_enc: EncodedDict,
        pos: int,
        field: str,
    ):
        errmsg = f"{msg}: field {field} pos {pos}"
        ValueError.__init__(self, errmsg)
        self.msg = msg
        self.s = s
        self.doc_dec = doc_dec
        self.doc_enc = doc_enc
        self.field = field
        self.pos = pos

    def __reduce__(
        self,
    ) -> Tuple[
        Type["DecodeError"],
        Tuple[str, Union[bytes, bytearray], DecodedDict, EncodedDict, int, str],
    ]:
        return (
            self.__class__,
            (self.msg, self.s, self.doc_dec, self.doc_enc, self.pos, self.field),
        )
```

--------------------------------

### iso8583.pp

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/functions.rst.txt

Helper function to pretty-print ISO 8583 messages.

```APIDOC
## iso8583.pp(data)

### Description
Prints a human-readable representation of an ISO 8583 message.

### Parameters
- **data** (dict/str) - The message to format and print.
```

--------------------------------

### Define ASCII Field with Binary Length

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a 16-byte ASCII field that uses binary length encoding.

```python
specification["2"] = {
    "data_enc": "ascii",
    "len_enc": "b",
    "len_type": 1,
    "max_len": 16,
    "desc": "ASCII field with binary length, e.g. \x101234567890123456"
}
```

--------------------------------

### Field Length and Data Parsing Logic

Source: https://pyiso8583.readthedocs.io/en/latest/_modules/iso8583/decoder.html

Handles conversion between nibbles and bytes for field length and extracts raw data from the byte array.

```python
# Encoded field length can be in bytes or half bytes (nibbles)
    # Convert nibbles to bytes if needed
    if len_count == "nibbles":
        if enc_field_len & 1:
            byte_field_len = (enc_field_len + 1) // 2
        else:
            byte_field_len = enc_field_len // 2
    else:
        byte_field_len = enc_field_len

    # Parse field data
    doc_enc[field_key]["data"] = bytes(s[idx : idx + byte_field_len])
    if len(doc_enc[field_key]["data"]) != byte_field_len:
        if len_count == "nibbles":
            actual_field_len = len(doc_enc[field_key]["data"]) * 2
        else:
            actual_field_len = len(doc_enc[field_key]["data"])

        raise DecodeError(
            f"Field data is {actual_field_len} {len_count}, expecting {enc_field_len}",
            s,
            doc_dec,
            doc_enc,
            idx,
            field_key,
        )

    if field_spec["data_enc"] == "b":
        doc_dec[field_key] = doc_enc[field_key]["data"].hex().upper()
        if len_count == "nibbles" and enc_field_len & 1:
            doc_dec[field_key] = _remove_pad_field(
                s,
                idx,
                doc_dec,
                doc_enc,
                field_key,
                field_spec,
                enc_field_len,
            )
    else:
        doc_dec[field_key] = _decode_text_data(
            s,
            doc_enc[field_key]["data"],
            idx,
            doc_dec,
            doc_enc,
            field_key,
            field_spec,
        )

    return idx + byte_field_len
```

--------------------------------

### Define Binary Primary Bitmap Field

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a binary primary bitmap field with a fixed length of 8 bytes.

```python
specification["p"] = {
    "data_enc": "b",
    "len_enc": "ascii",
    "len_type": 0,
    "max_len": 8,
    "desc": "Binary bitmap, e.g. \x12\x34\x56\x78\x90\xAB\xCD\xEF"
}
```

--------------------------------

### Overwrite existing bitmap

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

Shows that manually specified primary or secondary bitmaps are automatically overwritten with the correct values during encoding.

```python
>>> decoded = {
...     't': '0200',
...     'p': 'spam',
...     '1': 'eggs',
...     '102': '111111'}
>>> encoded_raw, encoded = iso8583.encode(decoded, spec)
>>> encoded_raw
bytearray(b'02008000000000000000000000000400000006111111')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'8000000000000000'},
 '1': {'len': b'', 'data': b'0000000004000000'},
 '102': {'len': b'06', 'data': b'111111'}}
>>> pprint.pp(decoded)
{'t': '0200', 'p': '8000000000000000', '102': '111111', '1': '0000000004000000'}
```

--------------------------------

### Convert JSON back to ISO8583

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

Deserialize JSON strings back into dictionaries for encoding into ISO8583 raw bytes.

```python
>>> encoded_raw, encoded = iso8583.encode(json.loads(decoded_json), spec)
>>> encoded_raw
bytearray(b'0200600008000000000014cardholder PAN111111021')
```

--------------------------------

### Define Hex String Primary Bitmap Field

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a hex string primary bitmap field with a fixed length of 16 bytes.

```python
specification["p"] = {
    "data_enc": "ascii",
    "len_enc": "ascii",
    "len_type": 0,
    "max_len": 16,
    "desc": "Hex string bitmap, e.g 1234567890ABCDEF"
}
```

--------------------------------

### Convert ISO8583 to and from JSON

Source: https://pyiso8583.readthedocs.io/en/latest/_sources/howto.rst.txt

Serialize decoded ISO8583 messages to JSON strings and reconstruct them for encoding. Specifications can also be serialized to JSON for portability.

```python
>>> import json
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> encoded_raw = b'0200600008000000000014cardholder PAN111111021'
>>> decoded, encoded = iso8583.decode(encoded_raw, spec)
>>> pprint.pp(decoded)
{'t': '0200',
 'p': '6000080000000000',
 '2': 'cardholder PAN',
 '3': '111111',
 '21': '021'}
>>> decoded_json = json.dumps(decoded)
>>> decoded_json
'{"t": "0200", "p": "6000080000000000", "2": "cardholder PAN", "3": "111111", "21": "021"}'
```

```python
>>> encoded_raw, encoded = iso8583.encode(json.loads(decoded_json), spec)
>>> encoded_raw
bytearray(b'0200600008000000000014cardholder PAN111111021')
```

```python
>>> import json
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> spec_json = json.dumps(spec)
>>> decoded = {
...     't': '0200',
...     '2': 'PAN'}
>>> encoded_raw, encoded = iso8583.encode(decoded, json.loads(spec_json))
>>> encoded_raw
bytearray(b'0200400000000000000003PAN')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'4000000000000000'},
 '2': {'len': b'03', 'data': b'PAN'}}
>>> pprint.pp(decoded)
{'t': '0200', '2': 'PAN', 'p': '4000000000000000'}
```

--------------------------------

### Encode Text Fields

Source: https://pyiso8583.readthedocs.io/en/latest/_modules/iso8583/encoder.html

Encodes an individual ISO8583 field using the specified character encoding.

```python
def _encode_text_field(
    doc_dec: DecodedDict,
    doc_enc: EncodedDict,
    field_data: str,
    field_key: str,
    field_spec: _FieldSpecDict,
    len_count: str,
) -> Tuple[bytes, int]:
    r"""Encode ISO8583 individual field.

    Parameters
    ----------
    doc_dec : dict
        Dict containing decoded ISO8583 data
    doc_enc : dict
        Dict containing encoded ISO8583 data
    field_data : str
        Field data to encode
    field_key : str
        Field ID to be encoded
    field_spec : dict
        A Python dict defining ISO8583 specification for this field.
        See :mod:`iso8583.specs` module for examples.

    Returns
    -------
    tuple(bytes, int)
        Encoded data and length of the encoded ISO8583 field data. The length is either nibbles or bytes.

    Raises
    ------
    EncodeError
        An error encoding ISO8583 bytearray.
    """
    try:
        encoded_data = field_data.encode(field_spec["data_enc"])
    except LookupError:
        raise EncodeError(
            "Failed to encode field, unknown encoding specified",
            doc_dec,
            doc_enc,
            field_key,
        ) from None
    except Exception:
        raise EncodeError(
            "Failed to encode field, invalid data",
            doc_dec,
            doc_enc,
            field_key,
        ) from None

    # Encoded field length can be in bytes or half bytes (nibbles)
    # Encoded nibble length directly corresponds to the count of received nibbles.
    if len_count == "nibbles":
        return (encoded_data, len(encoded_data) * 2)
    else:
        return (encoded_data, len(encoded_data))
```

--------------------------------

### Define Fixed Length Binary or BCD Field

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a 10-byte fixed length field using binary or BCD encoding.

```python
specification["2"] = {
    "data_enc": "b",
    "len_enc": "ascii",
    "len_type": 0,
    "max_len": 10,
    "desc": "Binary or BCD fixed field"
}
```

--------------------------------

### Define Nibble-based LLVAR Field with Padding

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a binary or BCD LLVAR field measured in nibbles, including left-padding with '0'.

```python
specification["5"] = {
    "data_enc": "b",
    "len_enc": "bcd",
    "len_type": 1,
    "len_count": "nibbles",
    "left_pad": "0",
    "max_len": 20,
    "desc": "Binary or BCD LLVAR field measured in nibbles, e.g. \x03\x01\x11"
}
```

--------------------------------

### Define Fixed Length Nibble Field with Right Padding

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures a 3-nibble fixed length field with right-padding using '0'.

```python
specification["6"] = {
    "data_enc": "b",
    "len_enc": "ascii",
    "len_type": 0,
    "len_count": "nibbles",
    "right_pad": "0",
    "max_len": 3,
    "desc": "Binary or BCD fixed field measured in nibbles, e.g. \x11\x10"
}
```

--------------------------------

### iso8583.encode(doc_dec, spec)

Source: https://pyiso8583.readthedocs.io/en/latest/functions.html

Serialize a Python dictionary containing ISO8583 data into a bytearray.

```APIDOC
## iso8583.encode(doc_dec, spec)

### Description
Serialize Python dict containing ISO8583 data to a bytearray.

### Parameters
- **doc_dec** (dict) - Required - Dict containing decoded ISO8583 data
- **spec** (dict) - Required - A Python dict defining ISO8583 specification.

### Returns
- **s** (bytearray) - Encoded ISO8583 data
- **doc_enc** (dict) - Dict containing encoded ISO8583 data

### Raises
- **EncodeError** - An error encoding ISO8583 bytearray
- **TypeError** - doc_dec must be a dict instance
```

--------------------------------

### Serialize ISO8583 Specifications to JSON

Source: https://pyiso8583.readthedocs.io/en/latest/howto.html

ISO8583 specification objects are JSON compatible, allowing them to be serialized and reloaded for encoding operations.

```python
>>> import json
>>> import pprint
>>> import iso8583
>>> from iso8583.specs import default_ascii as spec
>>> spec_json = json.dumps(spec)
>>> decoded = {
...     't': '0200',
...     '2': 'PAN'}
>>> encoded_raw, encoded = iso8583.encode(decoded, json.loads(spec_json))
>>> encoded_raw
bytearray(b'0200400000000000000003PAN')
>>> pprint.pp(encoded)
{'t': {'len': b'', 'data': b'0200'},
 'p': {'len': b'', 'data': b'4000000000000000'},
 '2': {'len': b'03', 'data': b'PAN'}}
>>> pprint.pp(decoded)
{'t': '0200', '2': 'PAN', 'p': '4000000000000000'}
```

--------------------------------

### Define ASCII LLVAR Field

Source: https://pyiso8583.readthedocs.io/en/latest/specifications.html

Configures an ASCII LLVAR field with a maximum length of 20 bytes.

```python
specification["3"] = {
    "data_enc": "ascii",
    "len_enc": "ascii",
    "len_type": 2,
    "max_len": 20,
    "desc": "ASCII LLVAR field"
}
```