orderpulse 0.2.36

High-performance exchange feed parser and orderflow analytics engine with Rust and Python bindings

OrderPulse / fastreader

A high-performance Python library for reading NSE binary order/trade feed files and building orderbook snapshots.

fastreader is written in Rust and exposed to Python through PyO3. Heavy binary parsing and orderbook processing runs in Rust, while Python users get a clean and simple API.

---

What this library does

• Reads NSE binary feed files.
• Extracts order and trade messages.
• Supports both RAM-based and streaming-based reading.
• Builds token-wise orderbook state.
• Provides best bid, best ask, spread, mid price, top levels, and full depth.
• Gives Python-friendly dictionaries, strings, and CSV-style snapshot rows.
• Dynamically builds NSE feed file paths from segment, stream ID, and date components.

---

Architecture

FeedPathBuilder
      |
      +--> build()                  constructs path string from (segment, stream_id, day, month, year)
      |
      +--> build_and_verify()       same, but also checks file exists on disk
      |
      v
Binary Feed File
      |
      v
Rust Binary Parser
      |
      +--> MessageCacheReader       loads all messages into RAM
      |
      +--> StreamingBinaryLoader    reads one message at a time from disk
      |
      v
Decoded Order / Trade Messages
      |
      v
OrderbookBuilder
      |
      +--> apply_filter()
      +--> build_from_list()
      +--> build_from_source()
      +--> orderbook_add_msg()
      |
      v
Snapshot / Full Depth / CSV Row

---

Classes

Class	Role	Best use case
FeedPathBuilder	Constructs NSE feed file paths from date and segment	Building file paths without hardcoding strings
MessageCacheReader	Loads the full file into memory	Backtesting, repeated analysis, small or medium files
StreamingBinaryLoader	Reads messages sequentially from disk	Very large files, Jupyter usage, low-memory processing
OrderbookBuilder	Builds and queries the orderbook	Snapshot generation and market-depth analysis

---

Installation / Import

After building and installing the wheel:

from fastreader import MessageCacheReader, StreamingBinaryLoader, OrderbookBuilder, FeedPathBuilder

Build locally with maturin:

maturin develop --release

Or build a wheel:

maturin build --release

---

Message types

Message type	Meaning	Packet
N	New order	Order
M	Modify order	Order
X	Cancel/delete order	Order
T	Trade	Trade

Order side values:

Side	Meaning
B	Buy / bid
S	Sell / ask

---

Quick Start: Build a file path dynamically

Use FeedPathBuilder to avoid hardcoding file paths.

from fastreader import FeedPathBuilder

b = FeedPathBuilder()

# Build path without checking disk
path = b.build("NSE_CM", stream_id=2, day=29, month=12, year=2025)
print(path)
# /nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin

# Build and verify the file exists
path = b.build_and_verify("NSE_CM", stream_id=2, day=29, month=12, year=2025)

# Custom base path
path = b.build("NSE_FO", stream_id=1, day=1, month=6, year=2026, base_path="/mnt/data")
print(path)
# /mnt/data/NSE_FO/Feed_FO_StreamID_1_01_06_2026.bin

---

Quick Start: Fast streaming for large files

Use this approach when the file is large and Jupyter becomes slow.

from fastreader import StreamingBinaryLoader, OrderbookBuilder

file_path = "/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin"

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
processed = builder.build_from_source(reader, limit=100000)

print("Processed:", processed)
print(builder.get_snapshot(token=1001, levels=5))

Expected output shape:

Processed: 100000
{
    'token': 1001,
    'found': True,
    'mid_price': 1050,
    'best_bid': (1000, 40),
    'best_ask': (1100, 15),
    'spread': 100,
    'bids': [(1000, 40), (995, 20)],
    'asks': [(1100, 15), (1110, 25)]
}

Actual values depend on your binary file and token.

---

1. FeedPathBuilder

FeedPathBuilder constructs NSE feed file paths from individual components: segment, stream ID, day, month, and year.

This avoids hardcoded path strings and keeps date formatting consistent with the NSE naming convention.

Path format produced:

{base_path}/{SEGMENT_FOLDER}/Feed_{SEGMENT_SHORT}_StreamID_{id}_{DD}_{MM}_{YYYY}.bin

Default base path: /nas/50.30

---

1.1 Create builder

from fastreader import FeedPathBuilder

b = FeedPathBuilder()

Expected output: no output.

---

1.2 build(segment, stream_id, day, month, year, base_path=None)

Constructs and returns a file path string. Does not check whether the file exists.

path = b.build(segment, stream_id, day, month, year, base_path=None)

Parameters:

Name	Type	Default	Meaning
segment	str	Required	"NSE_CM", "CM", "NSE_FO", or "FO" (case-insensitive)
stream_id	int	Required	Stream identifier, must be greater than 0
day	int	Required	Day of month, 1–31
month	int	Required	Month, 1–12
year	int	Required	Four-digit year, 2000–2100
base_path	str or None	None	Root directory; defaults to /nas/50.30

Returns:

Type	Meaning
str	Full file path

Raises RuntimeError on invalid inputs (bad segment, stream_id ≤ 0, out-of-range date).

Example:

b = FeedPathBuilder()

print(b.build("NSE_CM", stream_id=2, day=29, month=12, year=2025))
# /nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin

print(b.build("NSE_FO", stream_id=1, day=1, month=6, year=2026, base_path="/mnt/data"))
# /mnt/data/NSE_FO/Feed_FO_StreamID_1_01_06_2026.bin

print(b.build("CM", stream_id=5, day=3, month=1, year=2025))
# /nas/50.30/NSE_CM/Feed_CM_StreamID_5_03_01_2025.bin

---

1.3 build_and_verify(segment, stream_id, day, month, year, base_path=None)

Same as build(), but also checks that the constructed path exists on disk.

path = b.build_and_verify(segment, stream_id, day, month, year, base_path=None)

Parameters: same as build().

Returns:

Type	Meaning
str	Full file path (file confirmed to exist)

Raises RuntimeError if the file does not exist.

Example:

b = FeedPathBuilder()
try:
    path = b.build_and_verify("NSE_CM", stream_id=2, day=29, month=12, year=2025)
    print("File ready:", path)
except RuntimeError as e:
    print("File not found:", e)

Expected output when file exists:

File ready: /nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin

Expected error when file is missing:

RuntimeError: file not found: /nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin

---

2. MessageCacheReader

MessageCacheReader loads all decoded messages into RAM.

Use it when you want to repeatedly inspect the same file or run backtests on a manageable file size.

Avoid it for very large files because RAM usage increases with message count.

1.1 Create reader

from fastreader import MessageCacheReader

reader = MessageCacheReader()

Expected output: no output. It creates an empty reader.

---

1.2 load_to_cache(file_path)

Loads all supported messages from a binary file into memory.

count = reader.load_to_cache(file_path)

Parameters:

Name	Type	Meaning
file_path	str	Full path of the binary file

Returns:

Type	Meaning
int	Number of messages loaded

Example:

reader = MessageCacheReader()
count = reader.load_to_cache("/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin")
print("Loaded messages:", count)

Expected output:

Loaded messages: 1250000

---

1.3 get_all_messages()

Returns all cached order and trade messages as formatted strings.

messages = reader.get_all_messages()

Example:

messages = reader.get_all_messages()
print(messages[0])
print(messages[1])

Expected output:

Order Message: SeqNo 42, MsgLen 10, MsgType 'N', ExchTs 100000, LocalTs 200000, OrderId 55, Token 1001, Side 'B', Price 500, Quantity 100, Missed 0
Trade Message: SeqNo 99, MsgLen 10, MsgType 'T', ExchTs 300000, LocalTs 400000, BuyOrderId 10, SellOrderId 20, Token 5000, Price 750, Quantity 30, Missed 1

---

1.4 get_order_message()

Returns only order messages.

orders = reader.get_order_message()

Example:

orders = reader.get_order_message()
print("Order messages:", len(orders))
print(orders[0])

Expected output:

Order messages: 900000
Order Message: SeqNo 42, MsgLen 10, MsgType 'N', ExchTs 100000, LocalTs 200000, OrderId 55, Token 1001, Side 'B', Price 500, Quantity 100, Missed 0

Note: the current API name is get_order_message(), not get_all_order_message().

---

1.5 get_trade_message()

Returns only trade messages.

trades = reader.get_trade_message()

Example:

trades = reader.get_trade_message()
print("Trade messages:", len(trades))
print(trades[0])

Expected output:

Trade messages: 350000
Trade Message: SeqNo 99, MsgLen 10, MsgType 'T', ExchTs 300000, LocalTs 400000, BuyOrderId 10, SellOrderId 20, Token 5000, Price 750, Quantity 30, Missed 1

---

1.6 get_all_trade_message()

Alias for get_trade_message().

trades = reader.get_all_trade_message()

Example:

trades = reader.get_all_trade_message()
print(trades[:2])

Expected output:

[
  "Trade Message: SeqNo 99, MsgLen 10, MsgType 'T', ExchTs 300000, LocalTs 400000, BuyOrderId 10, SellOrderId 20, Token 5000, Price 750, Quantity 30, Missed 1"
]

---

1.7 get_cache_summary()

Returns a Python dictionary with cache statistics.

summary = reader.get_cache_summary()

Returned keys:

Key	Meaning
file_source	File path loaded into cache
total_messages	Total messages cached
total_orders	Total order messages
total_trades	Total trade messages
memory_usage_bytes	Estimated memory usage

Example:

summary = reader.get_cache_summary()
print(summary)

Expected output:

{
    'file_source': '/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin',
    'total_messages': 1250000,
    'total_orders': 900000,
    'total_trades': 350000,
    'memory_usage_bytes': 80000000
}

---

3. StreamingBinaryLoader

StreamingBinaryLoader opens the binary file and reads messages one by one from disk.

This is the recommended class for large files.

3.1 Create loader

from fastreader import StreamingBinaryLoader

reader = StreamingBinaryLoader()

Expected output: no output.

---

3.2 open_stream(file_path, count_messages=True)

Opens a binary file for sequential reading.

count = reader.open_stream(file_path, count_messages=True)

Parameters:

Name	Type	Default	Meaning
file_path	str	Required	Full binary file path
count_messages	bool	True	Whether to scan the file and count messages

Returns:

Case	Return
count_messages=True	Total message count
count_messages=False	0 immediately

For very large files, prefer:

reader.open_stream(file_path, count_messages=False)

This opens faster because it skips the full count scan.

Example:

reader = StreamingBinaryLoader()
count = reader.open_stream("/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin", count_messages=False)
print("Count:", count)

Expected output:

Count: 0

Important: 0 does not mean the file is empty. It means counting was skipped.

---

3.3 get_next_message()

Reads the next message and returns a formatted string.

msg = reader.get_next_message()

Returns:

Return	Meaning
Formatted string	Next order/trade message
"END"	End of file

Example:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

print(reader.get_next_message())
print(reader.get_next_message())
print(reader.get_next_message())

Expected output:

Order Message: SeqNo 1, MsgLen 10, MsgType 'N', ExchTs 100001, LocalTs 200001, OrderId 10, Token 200, Side 'B', Price 100, Quantity 5, Missed 0
Order Message: SeqNo 2, MsgLen 10, MsgType 'N', ExchTs 100002, LocalTs 200002, OrderId 20, Token 200, Side 'B', Price 101, Quantity 8, Missed 0
Trade Message: SeqNo 3, MsgLen 10, MsgType 'T', ExchTs 300003, LocalTs 400003, BuyOrderId 10, SellOrderId 20, Token 200, Price 100, Quantity 5, Missed 0

---

3.4 get_next_msg()

Reads the next message and returns a Python dictionary instead of a string.

This is the best method when you want to pass one message to OrderbookBuilder.orderbook_add_msg().

msg = reader.get_next_msg()

Returns:

Return	Meaning
dict	Next decoded message
None	End of file

Example:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

msg = reader.get_next_msg()
print(msg)

Expected order-message output:

{
    'message_kind': 'order',
    'seq_no': 1,
    'msg_len': 10,
    'stream_id': 2,
    'msg_type': 'N',
    'exch_ts': 100001,
    'local_ts': 200001,
    'order_id': 10,
    'token': 200,
    'order_type': 'B',
    'price': 100,
    'quantity': 5,
    'flags': False
}

Expected trade-message output:

{
    'message_kind': 'trade',
    'seq_no': 3,
    'msg_len': 10,
    'stream_id': 2,
    'msg_type': 'T',
    'exch_ts': 300003,
    'local_ts': 400003,
    'buy_order_id': 10,
    'sell_order_id': 20,
    'token': 200,
    'trade_price': 100,
    'trade_quantity': 5,
    'flags': False
}

---

3.5 reset_cursor()

Moves the stream cursor back to the beginning of the file.

reader.reset_cursor()

Example:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

first = reader.get_next_message()
second = reader.get_next_message()

reader.reset_cursor()
first_again = reader.get_next_message()

print(first == first_again)

Expected output:

True

---

4. OrderbookBuilder

OrderbookBuilder processes decoded messages and maintains orderbook state.

It can build from:

• MessageCacheReader
• StreamingBinaryLoader
• List of decoded Python dictionaries
• One message at a time using orderbook_add_msg()

---

4.1 Create builder

from fastreader import OrderbookBuilder

builder = OrderbookBuilder()

Expected output: no output.

---

4.2 apply_filter(logic_criteria=None)

Filters which message types should be processed.

builder.apply_filter(["N", "M", "X"])

Parameters:

Value	Meaning
None	Process all supported messages
["N"]	Process only new orders
["N", "M", "X"]	Process order messages only
["T"]	Process trades only

Example:

builder = OrderbookBuilder()
builder.apply_filter(["N", "M", "X"])

Expected output: no output. The filter is stored inside builder.

Clear filter:

builder.apply_filter(None)

---

4.3 build_from_source(source, limit=None)

Builds orderbook from a reader object.

Accepted sources:

• MessageCacheReader
• StreamingBinaryLoader

processed = builder.build_from_source(source, limit=None)

Parameters:

Name	Type	Meaning
source	reader object	Cache reader or streaming reader
limit	int or None	Maximum accepted messages to process from stream

Example with streaming:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
processed = builder.build_from_source(reader, limit=100000)

print("Processed:", processed)

Expected output:

Processed: 100000

Example with cache:

reader = MessageCacheReader()
reader.load_to_cache(file_path)

builder = OrderbookBuilder()
processed = builder.build_from_source(reader)

print("Processed:", processed)

Expected output:

Processed: 1250000

---

4.4 build_from_list(source)

Builds the orderbook from either:

1. A MessageCacheReader
2. A Python list[dict] of decoded messages

processed = builder.build_from_list(source)

Example with MessageCacheReader:

reader = MessageCacheReader()
reader.load_to_cache(file_path)

builder = OrderbookBuilder()
processed = builder.build_from_list(reader)

print("Processed:", processed)

Expected output:

Processed: 1250000

Example with list of dictionaries:

messages = [
    {
        "msg_type": "N",
        "exch_ts": 100000,
        "order_id": 1,
        "token": 777,
        "order_type": "B",
        "price": 1000,
        "quantity": 40,
        "local_ts": 200000,
        "flags": False,
    },
    {
        "msg_type": "N",
        "exch_ts": 100001,
        "order_id": 2,
        "token": 777,
        "order_type": "S",
        "price": 1100,
        "quantity": 15,
        "local_ts": 200001,
        "flags": False,
    },
]

builder = OrderbookBuilder()
processed = builder.build_from_list(messages)
print("Processed:", processed)

Expected output:

Processed: 2

---

4.5 orderbook_add_msg(msg)

Processes exactly one already-decoded message dictionary.

This function expects one message returned by reader.get_next_msg().

processed = builder.orderbook_add_msg(msg)

Returns:

Return	Meaning
True	Message was accepted and applied
False	Message was valid but skipped by filter/business rules

Correct usage:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()

msg = reader.get_next_msg()
if msg is not None:
    processed = builder.orderbook_add_msg(msg)
    print("Processed:", processed)

Expected output:

Processed: True

Loop usage:

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()

while True:
    msg = reader.get_next_msg()
    if msg is None:
        break
    builder.orderbook_add_msg(msg)

print(builder.get_snapshot(token=1001, levels=5))

Important: do not pass the reader object directly to orderbook_add_msg(). Pass one decoded message dictionary.

Wrong:

builder.orderbook_add_msg(reader)   # wrong

Right:

msg = reader.get_next_msg()
builder.orderbook_add_msg(msg)      # right

---

4.6 get_snapshot(token, levels=None)

Returns top bid/ask levels for one token.

snapshot = builder.get_snapshot(token=1001, levels=5)

Parameters:

Name	Type	Default	Meaning
token	int	Required	Instrument token
levels	int or None	5	Number of bid/ask levels

Returns dictionary:

Key	Meaning
token	Requested token
found	Whether orderbook exists for token
mid_price	(best_bid + best_ask) / 2 when available
best_bid	Best bid tuple (price, quantity)
best_ask	Best ask tuple (price, quantity)
spread	best_ask_price - best_bid_price
bids	Top bid levels
asks	Top ask levels

Example:

snapshot = builder.get_snapshot(token=777, levels=5)
print(snapshot)

Expected output:

{
    'token': 777,
    'found': True,
    'mid_price': 1050,
    'best_bid': (1000, 40),
    'best_ask': (1100, 15),
    'spread': 100,
    'bids': [(1000, 40)],
    'asks': [(1100, 15)]
}

If token is not found:

{
    'token': 99999,
    'found': False,
    'mid_price': 0,
    'best_bid': None,
    'best_ask': None,
    'spread': None,
    'bids': [],
    'asks': []
}

---

4.7 get_orderbook_snapshot(token, levels=None)

Alias for get_snapshot().

snapshot = builder.get_orderbook_snapshot(token=1001, levels=5)

Expected output is the same as get_snapshot().

---

4.8 get_full_depth(token)

Returns full available depth for one token.

depth = builder.get_full_depth(token=1001)

Returns dictionary:

Key	Meaning
token	Requested token
found	Whether token was found
best_bid	Best bid level
best_ask	Best ask level
spread	Ask minus bid
bids	All bid levels
asks	All ask levels

Example:

depth = builder.get_full_depth(token=777)
print(depth)

Expected output:

{
    'token': 777,
    'found': True,
    'best_bid': (1000, 40),
    'best_ask': (1100, 15),
    'spread': 100,
    'bids': [(1000, 40), (995, 20), (990, 10)],
    'asks': [(1100, 15), (1110, 25), (1120, 30)]
}

---

4.9 snapshot_header()

Returns CSV header for snapshot rows.

header = builder.snapshot_header()

Example:

print(builder.snapshot_header())

Expected output:

local_ts,exch_ts,mid_price,bid_price_0,bid_qty_0,ask_price_0,ask_qty_0,bid_price_1,bid_qty_1,ask_price_1,ask_qty_1,bid_price_2,bid_qty_2,ask_price_2,ask_qty_2,bid_price_3,bid_qty_3,ask_price_3,ask_qty_3,bid_price_4,bid_qty_4,ask_price_4,ask_qty_4

---

4.10 get_snapshot_row(token, levels=None)

Returns one CSV-style row for a token snapshot.

row = builder.get_snapshot_row(token=1001, levels=5)

Example:

print(builder.snapshot_header())
print(builder.get_snapshot_row(token=777, levels=5))

Expected output:

local_ts,exch_ts,mid_price,bid_price_0,bid_qty_0,ask_price_0,ask_qty_0,bid_price_1,bid_qty_1,ask_price_1,ask_qty_1,bid_price_2,bid_qty_2,ask_price_2,ask_qty_2,bid_price_3,bid_qty_3,ask_price_3,ask_qty_3,bid_price_4,bid_qty_4,ask_price_4,ask_qty_4
0,0,1050,1000,40,1100,15,995,20,1110,25,990,10,1120,30,0,0,0,0,0,0,0,0

---

Recommended Workflows

Workflow A: Large file, fastest Jupyter usage

from fastreader import StreamingBinaryLoader, OrderbookBuilder

file_path = "/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin"

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
processed = builder.build_from_source(reader, limit=500000)

print("Processed:", processed)
print(builder.get_snapshot(token=1001, levels=5))

Why this is fast:

• File is not loaded into RAM.
• Message counting is skipped.
• Rust reads and processes messages directly.

---

Workflow B: Load once, analyze many times

from fastreader import MessageCacheReader, OrderbookBuilder

reader = MessageCacheReader()
count = reader.load_to_cache(file_path)

print(reader.get_cache_summary())

builder = OrderbookBuilder()
processed = builder.build_from_source(reader)

print(builder.get_snapshot(token=1001, levels=5))

Use this when the file fits comfortably in RAM.

---

Workflow C: Process one message at a time

from fastreader import StreamingBinaryLoader, OrderbookBuilder

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()

while True:
    msg = reader.get_next_msg()
    if msg is None:
        break

    accepted = builder.orderbook_add_msg(msg)

print(builder.get_snapshot(token=1001, levels=5))

Use this when you want full control over each message.

---

Workflow D: Build path then stream

from fastreader import FeedPathBuilder, StreamingBinaryLoader, OrderbookBuilder

b = FeedPathBuilder()
file_path = b.build_and_verify("NSE_CM", stream_id=2, day=29, month=12, year=2025)

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
processed = builder.build_from_source(reader)

print("Processed:", processed)
print(builder.get_snapshot(token=1001, levels=5))

Use this to avoid any hardcoded path in your script.

---

Workflow E: Only process order messages

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
builder.apply_filter(["N", "M", "X"])

processed = builder.build_from_source(reader)
print("Processed order messages:", processed)

---

Workflow F: Only process new orders

builder = OrderbookBuilder()
builder.apply_filter(["N"])

---

Error Handling

File does not exist

reader = StreamingBinaryLoader()
reader.open_stream("/wrong/path/file.bin")

Expected error:

RuntimeError: No such file or directory

Invalid binary file

If the first valid message type is not one of T, N, M, or X, the library raises an error.

Expected error shape:

RuntimeError: invalid first message type: <value>

Passing wrong object to orderbook_add_msg()

Wrong:

builder.orderbook_add_msg(reader)

Expected error:

TypeError: orderbook_add_msg expects one message dict from get_next_msg()

Right:

msg = reader.get_next_msg()
builder.orderbook_add_msg(msg)

---

Performance Tips

For very large files

Use:

reader.open_stream(file_path, count_messages=False)

Do not use load_to_cache() unless you have enough RAM.

For fastest orderbook building

Use:

builder.build_from_source(reader)

This keeps the processing path simple and Rust-heavy.

For debugging first few messages

Use:

print(reader.get_next_message())
print(reader.get_next_message())
print(reader.get_next_message())

For Python-level custom logic

Use:

msg = reader.get_next_msg()
builder.orderbook_add_msg(msg)

This gives Python access to every decoded message.

---

Complete Example

from fastreader import StreamingBinaryLoader, OrderbookBuilder

file_path = "/nas/50.30/NSE_CM/Feed_CM_StreamID_2_29_12_2025.bin"
token = 1001

reader = StreamingBinaryLoader()
reader.open_stream(file_path, count_messages=False)

builder = OrderbookBuilder()
builder.apply_filter(["N", "M", "X", "T"])

processed = builder.build_from_source(reader, limit=1000000)

print("Processed:", processed)
print("Snapshot:")
print(builder.get_snapshot(token=token, levels=5))

print("CSV:")
print(builder.snapshot_header())
print(builder.get_snapshot_row(token=token, levels=5))

Expected output shape:

Processed: 1000000
Snapshot:
{'token': 1001, 'found': True, 'mid_price': 1050, 'best_bid': (1000, 40), 'best_ask': (1100, 15), 'spread': 100, 'bids': [(1000, 40)], 'asks': [(1100, 15)]}
CSV:
local_ts,exch_ts,mid_price,bid_price_0,bid_qty_0,ask_price_0,ask_qty_0,bid_price_1,bid_qty_1,ask_price_1,bid_qty_1,...
0,0,1050,1000,40,1100,15,0,0,0,0,...

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API Summary

FeedPathBuilder

Function	Description
build(segment, stream_id, day, month, year, base_path=None)	Return constructed file path string
build_and_verify(segment, stream_id, day, month, year, base_path=None)	Same, but raises RuntimeError if file does not exist

MessageCacheReader

Function	Description
load_to_cache(file_path)	Load full binary file into memory
get_all_messages()	Return all cached messages as strings
get_order_message()	Return only order messages
get_trade_message()	Return only trade messages
get_all_trade_message()	Alias for trade messages
get_cache_summary()	Return file, count, and memory summary

StreamingBinaryLoader

Function	Description
open_stream(file_path, count_messages=True)	Open binary file for streaming
get_next_message()	Return next message as formatted string
get_next_msg()	Return next message as Python dictionary
reset_cursor()	Move cursor back to start of file

OrderbookBuilder

Function	Description
apply_filter(logic_criteria=None)	Filter message types
orderbook_add_msg(msg)	Process one decoded message dictionary
build_from_list(source)	Build from cache reader or list of dict messages
build_from_source(source, limit=None)	Build from cache reader or stream reader
get_snapshot(token, levels=None)	Return top-N orderbook levels
get_orderbook_snapshot(token, levels=None)	Alias for get_snapshot()
get_full_depth(token)	Return full depth for token
snapshot_header()	Return CSV snapshot header
get_snapshot_row(token, levels=None)	Return CSV snapshot row

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Notes for Python users

• Use FeedPathBuilder to construct NSE file paths from date and segment instead of hardcoding strings.
• Use build_and_verify() to catch missing files early before opening a stream.
• Use StreamingBinaryLoader for huge files.
• Use count_messages=False when opening huge files in Jupyter.
• Use MessageCacheReader only when the file comfortably fits in RAM.
• Use build_from_source() for simple and fast orderbook building.
• Use get_next_msg() plus orderbook_add_msg() when you need custom Python logic per message.
• Use get_snapshot() for Python dictionary output.
• Use snapshot_header() and get_snapshot_row() for CSV-style output.

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License

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