Features

• Pure Python, zero runtime dependencies
• Pack and unpack ISO-8583 messages
• Fixed and variable-length fields (LLVAR, LLLVAR)
• Many field formats: ASCII, BCD, and raw binary
• Nested subfields, including ASCII TLV and repeatable subfields
• Partial unpacking that stops at the first error
• Bring-your-own MTI and LengthType enums

Table of contents

• Quick start
• Field formats
• Length types
• Subfields
• Partial unpack
• Custom MTI
• Custom LengthType
• License

Quick start

from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import MTI, LengthType
from iso_8583 import FieldSpec, Message
 
spec = {
    2: FieldSpec(LengthType.LLVAR, FieldFormat.N, 19),
    3: FieldSpec(LengthType.FIXED, FieldFormat.N, 6),
    4: FieldSpec(LengthType.FIXED, FieldFormat.N, 12),
    41: FieldSpec(LengthType.FIXED, FieldFormat.ANSP, 8),
}
 
msg = Message(spec, MTI.AUTHORISATION_REQUEST)
msg[2] = "4242424242424242"
msg[3] = "000000"
msg[4] = "000000001000"
msg[41] = "TERM0001"
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw)
 
print(msg2[2])   # 4242424242424242
print(msg2[41])  # TERM0001

Field formats

Length types

Subfields

from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import MTI, LengthType
from iso_8583 import FieldSpec, SubFieldSpec, Message
 
spec = {
    119: FieldSpec(
        LengthType.LLLVAR, FieldFormat.B, 255,
        subfields={
            "0001": SubFieldSpec(LengthType.FIXED, FieldFormat.AN, 1),
            "0009": SubFieldSpec(LengthType.LLVAR, FieldFormat.ANSP, 8),
            "0011": SubFieldSpec(LengthType.LLVAR, FieldFormat.N, 19),
        },
    ),
}
 
msg = Message(spec, MTI.AUTHORISATION_REQUEST)
msg[119] = {"0001": "A", "0009": "HELLO", "0011": "1234567890"}
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw)
print(msg2[119])
# {'0001': 'A', '0009': 'HELLO', '0011': '1234567890'}

For ASCII TLV subfields (tag 2 chars + length 2 chars + value), use TlvFieldSpec:

from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import MTI, LengthType
from iso_8583 import TlvFieldSpec, SubFieldSpec, Message
 
spec = {
    47: TlvFieldSpec(
        LengthType.LLVAR, FieldFormat.ANSP, 99,
        subfields={
            "T1": SubFieldSpec(LengthType.LLVAR, FieldFormat.ANSP, 10),
            "T2": SubFieldSpec(LengthType.LLVAR, FieldFormat.N, 8),
        },
    ),
}
 
msg = Message(spec, MTI.AUTHORISATION_REQUEST)
msg[47] = {"T1": "HELLO", "T2": "12345678"}
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw)
print(msg2[47])
# {'T1': 'HELLO', 'T2': '12345678'}

Repeatable subfields accept a list:

from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import MTI, LengthType
from iso_8583 import FieldSpec, SubFieldSpec, Message
 
spec = {
    56: FieldSpec(
        LengthType.LLVAR, FieldFormat.B, 99,
        subfields={
            "0001": SubFieldSpec(LengthType.FIXED, FieldFormat.N, 4),
            "0023": SubFieldSpec(
                LengthType.FIXED, FieldFormat.ANSP, 8,
                repeatable=True,
            ),
        },
    ),
}
 
msg = Message(spec, MTI.AUTHORISATION_REQUEST)
msg[56] = {"0001": "1234", "0023": ["ENTRY-01", "ENTRY-02"]}
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw)
print(msg2[56]["0023"])
# ['ENTRY-01', 'ENTRY-02']

Partial unpack

Stops at the first error and returns what was read:

from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import MTI, LengthType
from iso_8583 import FieldSpec, Message
 
full_spec = {
    2: FieldSpec(LengthType.LLVAR, FieldFormat.N, 19),
    3: FieldSpec(LengthType.FIXED, FieldFormat.N, 6),
}
partial_spec = {
    2: FieldSpec(LengthType.LLVAR, FieldFormat.N, 19),
}
 
msg = Message(full_spec, MTI.AUTHORISATION_REQUEST)
msg[2] = "4242424242424242"
msg[3] = "000000"
raw = msg.pack()
 
result, error = Message.unpack_partial(partial_spec, raw)
print(result[2])  # 4242424242424242
print(error)      # bit 3: present in bitmap but not in spec

Custom MTI

Pass mti_class to unpack to get the MTI back as your own enum:

from enum import Enum
from iso_8583.fixed_formats import FieldFormat
from iso_8583.extendable_formats import LengthType
from iso_8583 import FieldSpec, Message
 
class MyMTI(int, Enum):
    SALE = 0x0200
    SALE_RESPONSE = 0x0210
    REVERSAL = 0x0400
 
spec = {2: FieldSpec(LengthType.LLVAR, FieldFormat.N, 19)}
 
msg = Message(spec, MyMTI.SALE)
msg[2] = "4242424242424242"
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw, mti_class=MyMTI)
print(msg2._mti)  # MyMTI.SALE

Custom LengthType

from enum import Enum
from iso_8583.fixed_formats import FieldFormat
from iso_8583 import FieldSpec, Message
 
class MyLengthType(Enum):
    FIXED = (0, None)
    LLVAR = (1, 99)
    LLLVAR = (1, 255)
    LL2VAR = (2, 999)
 
    def __init__(self, prefix_bytes, max_field_length):
        self.prefix_bytes = prefix_bytes
        self.max_field_length = max_field_length
 
class MyMTI(int, Enum):
    AUTH = 0x0100
 
spec = {
    2: FieldSpec(MyLengthType.LLVAR, FieldFormat.N, 19),
    60: FieldSpec(MyLengthType.LL2VAR, FieldFormat.ANSP, 999),
}
 
msg = Message(spec, MyMTI.AUTH)
msg[2] = "4242424242424242"
msg[60] = "HELLO WORLD"
 
raw = msg.pack()
msg2 = Message.unpack(spec, raw)
print(msg2[2])   # 4242424242424242
print(msg2[60])  # HELLO WORLD

License

See LICENSE.