Python Microsoft Fabric API - Files

onelake_list, onelake_read, onelake_write and onelake_delete, and the two forms a file path takes.

A connection has four methods for files. They read and write OneLake, the storage behind every lakehouse, directly - the Files section in the lakehouse explorer is the folder they work in. They use a second token, for storage rather than for the Fabric API, which the connection obtains and refreshes on its own alongside the first.

File paths

Every path starts with the lakehouse and continues into it, and the lakehouse can be named in two ways:

Form	Example
Name and type	`Operations.Lakehouse/Files/incoming/payments-2026-03.csv`
Item ID	`66666666-7777-8888-9999-000000000000/Files/incoming/payments-2026-03.csv`

Both forms work in every method below. Files is where a lakehouse keeps files, and Tables next to it is where its tables are stored, which the table methods manage.

onelake_list

conn.onelake_list(workspace_id, directory='')

Lists what is directly under a path - files and subfolders, without going into the subfolders.

Parameter	Type	Meaning
`workspace_id`	str	The workspace whose storage to list
`directory`	str	The folder to list, e.g. `Operations.Lakehouse/Files/incoming`, or empty for the top of the workspace

Returns a dict with paths, a list of dicts each with name (the full path), isDirectory (true or false), contentLength and lastModified.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ListFiles(Service):

    def handle(self):

        workspace_id = '11111111-2222-3333-4444-555555555555'

        conn = self.microsoft.fabric['My Fabric']

        listing = conn.onelake_list(workspace_id, 'Operations.Lakehouse/Files/incoming')

        files = []
        for path in listing['paths']:
            file = {'name': path['name'], 'is_directory': path['isDirectory']}
            files.append(file)

        self.response.payload = {'files': files}

{"files": [{"name": "Operations.Lakehouse/Files/incoming/payments-2026-03.csv", "is_directory": false}]}

onelake_read

conn.onelake_read(workspace_id, file_path)

Returns a file's contents as bytes.

Parameter	Type	Meaning
`workspace_id`	str	The workspace the file is in
`file_path`	str	The file, in either path form

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ReadFile(Service):

    def handle(self):

        workspace_id = '11111111-2222-3333-4444-555555555555'
        file_path = 'Operations.Lakehouse/Files/incoming/payments-2026-03.csv'

        conn = self.microsoft.fabric['My Fabric']

        data = conn.onelake_read(workspace_id, file_path)
        text = data.decode('utf-8')

        size = len(data)
        lines = text.splitlines()
        first_line = lines[0]

        self.response.payload = {'size': size, 'first_line': first_line}

{"size": 142, "first_line": "invoice_id,location,insurer,amount,status,sent_at"}

onelake_write

conn.onelake_write(workspace_id, file_path, data)

Creates a file with the given bytes, or replaces it if it exists. Folders on the way are created as needed.

Parameter	Type	Meaning
`workspace_id`	str	The workspace to write to
`file_path`	str	The file, in either path form
`data`	bytes	The contents

Returns nothing.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class WriteFile(Service):

    def handle(self):

        workspace_id = '11111111-2222-3333-4444-555555555555'
        file_path = 'Operations.Lakehouse/Files/exports/invoices-2026-03.csv'

        conn = self.microsoft.fabric['My Fabric']

        text = 'location,invoiced\nRiverside,2895.50\nOak Hill,1840.00\nMaple Grove,415.75\n'
        data = text.encode('utf-8')

        conn.onelake_write(workspace_id, file_path, data)

        self.response.payload = {'bytes': len(data)}

onelake_delete

conn.onelake_delete(workspace_id, file_path)

Deletes a file.

Parameter	Type	Meaning
`workspace_id`	str	The workspace the file is in
`file_path`	str	The file, in either path form

Returns nothing. Deleting a file that does not exist raises an exception.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class DeleteFile(Service):

    def handle(self):

        workspace_id = '11111111-2222-3333-4444-555555555555'
        file_path = 'Operations.Lakehouse/Files/incoming/payments-2026-03.csv'

        conn = self.microsoft.fabric['My Fabric']

        conn.onelake_delete(workspace_id, file_path)

Page	What it covers
Tables	Turning a written file into a table with load_table
Sending and receiving files	These methods at work on an incoming file and a monthly export
Connection	The storage token these methods use