backtrader.writer module

Writer Module - Output writing for strategy execution results.

This module provides classes for writing strategy execution results to files or stdout. It supports CSV output and custom formatting.

Classes:

WriterBase: Base class for writers. WriterFile: Writes execution results to file or stdout.

Example

Using WriterFile with cerebro: >>> cerebro = bt.Cerebro() >>> cerebro.addwriter(bt.WriterFile, out=’results.csv’, csv=True) >>> results = cerebro.run()

class backtrader.writer.WriterBase

Bases: ParameterizedBase

Base class for writers.

This is the base class for all writer implementations. Subclasses should override the writing methods to provide custom output formatting.

class backtrader.writer.WriterFile

Bases: WriterBase

The system-wide writer class.

Writes strategy execution results to a file or stdout.

Params:

out: Output stream (default: sys.stdout). If a string is passed,

it’s treated as a filename. Use None for multiprocess optimization.

close_out: If True, explicitly close the output stream (default: False). csv: If True, write CSV data during execution (default: False). csv_filternan: If True, replace NaN values with empty fields (default: True). csvsep: CSV separator character (default: ‘,’). indent: Indentation for formatted output (default: 2).

Example

>>> cerebro.addwriter(bt.WriterFile, out='results.csv', csv=True)

params = (('out', None), ('close_out', False), ('csv', False), ('csvsep', ','), ('csv_filternan', True), ('csv_counter', True), ('indent', 2), ('separators', ['=', '-', '+', '*', '.', '~', '"', '^', '#']), ('seplen', 79), ('rounding', None))

__init__(**kwargs)

Initialize the WriterFile instance.

Sets up the counter, headers list, and values list for tracking data during execution.

Parameters:

**kwargs – Keyword arguments for writer parameters.

start()

Initialize the writer at the start of execution.

Opens the output file/stream and writes CSV headers if CSV mode is enabled.

stop()

Close the output stream when execution ends.

Closes the output file if close_out parameter is True.

next()

Write accumulated values to output.

Called during execution to write the current set of values to the CSV output and reset the values list.

addheaders(headers)

Add column headers for CSV output.

Parameters:

headers – List of header names to add.

addvalues(values)

Add values to be written to CSV output.

Parameters:

values – Iterable of values to add.

writeiterable(iterable, func=None, counter='')

Write an iterable to the output as a CSV line.

Parameters:

• iterable – The data to write.

• func – Optional function to apply to each element.

• counter – Optional counter value to prepend.

writeline(line)

Write a single line to the output.

Parameters:

line – The line content to write.

writelines(lines)

Write multiple lines to the output.

Parameters:

lines – Iterable of line contents to write.

writelineseparator(level=0)

Write a separator line for visual formatting.

Parameters:

level – Indentation level that determines separator style.

writedict(dct, level=0, recurse=False)

Write a dictionary to the output with formatting.

Parameters:

• dct – Dictionary to write.

• level – Indentation level for nested output.

• recurse – Whether this is a recursive call.

class backtrader.writer.WriterStringIO

Bases: WriterFile

Writer that outputs to an in-memory StringIO buffer.

This writer stores all output in memory rather than writing to a file. Useful for testing or when you need to capture output programmatically.

_stringio

The StringIO buffer holding the output.

Example

>>> writer = WriterStringIO()
>>> cerebro.addwriter(writer)
>>> results = cerebro.run()
>>> output = writer.getvalue()

params = (('out', <class '_io.StringIO'>),)

__init__(**kwargs)

Initialize the WriterStringIO instance.

Creates a new StringIO buffer for storing output.

Parameters:

**kwargs – Keyword arguments for writer parameters.

property out

Always return our StringIO object.

stop()

Seek to beginning for reading.

getvalue()

Get the content from the StringIO object.