activity-parser

Parser for loading FIT, TCX and GPX activity files into Pandas DataFrames.

Provides a parser object for reading (optionally gzipped) FIT, TCX, and GPX activity files and converting them into Pandas DataFrames. During import, field names extracted from activity files are normalized into a canonical set of output column names with consistent units to allow for standardized downstream data processing.

Installation

pip install activity-parser

Usage

Create a new instance of the ActivityParser class to be reused for subsequent parsing of activity files:

import activity_parser

parser = activity_parser.ActivityParser()

Parse FIT, TCX and GPX files into normalized DataFrames:

from activity_parser import ParseError

try:
    records, laps, activity = parser.parse("path/to/fit_file.fit")
    records, laps, activity = parser.parse("path/to/gpx_file.gpx")
    records, laps, activity = parser.parse("path/to/tcx_file.tcx")
except ParseError as e:
    ...

Each file is assumed to contain a single activity. Multiple activities/tracks (chained FIT files, multi-activity TCX, multi-track GPX) have their records/laps merged into one set of results. In those cases, the returned Activity summary reflects only the first activity/session in the file.

parse() raises ParseError (FitError for FIT files, XmlError for TCX/GPX) when a file fails to parse. It raises ValueError for an unrecognized or ambiguous file type.

Output data

records and laps are each a DataFrame of normalized data, e.g.:

                           distance  speed  cadence  heart_rate
time
2026-01-05 08:00:00+00:00      0.00   36.0       80         100
2026-01-05 08:00:01+00:00      0.01   36.0       81         101

A few notes on column handling:

• Column names and units are standardized across source formats for known field types.
• Unknown fields are omitted by default; customize columns via record_columns, lap_columns, and include_all_columns on ActivityParser — see its docstring for details.
• Not every column appears in every file: parse() only includes columns actually present.

Records

Not all fields are available in all source formats. Fields marked with (*) are exporter-dependent.

Laps

GPX files have no lap data, so laps is always an empty DataFrame for GPX. Fields marked with (*) are exporter-dependent.

Activity

activity is an Activity dataclass instance: a small file-level summary. Fields are None when the source format/file doesn't record them. Values come from the file's own summary fields, never computed/derived from records or laps.

(*) GPX's start_time comes from metadata/time, which is technically the file's export time rather than the activity's start.

Parser notes

FIT files

FIT parsing wraps garmin-fit-sdk, Garmin's official SDK, which decodes against the public FIT SDK profile.

parse() transforms certain FIT fields beyond decoding:

• Positions are converted to degrees, distances to km, and speeds to km/h. Vertical rates (avg_vam, vertical_speed, and similar) stay in m/s.
• For fields with lower- and higher-precision versions, only the higher-precision value is returned, under the base field's name.
• For fields with sub-integer precision in a separate field, the precision is added into the base field.
• left_right_balance (a bit-packed field) is decoded into left_balance/right_balance.
• heart_rate is merged with a higher-rate hr stream when the file has one. Records outside its coverage keep their own device value.

Messages/fields that can't be resolved against the FIT profile (e.g. proprietary extensions) are kept as raw values under unknown_<n> names. Developer fields are resolved to their file-embedded names and flattened into ordinary columns alongside built-in fields.

parse_fit and parse_fit_raw are the lower-level functions ActivityParser.parse() wraps for FIT files. parse_fit returns the same canonical (records, laps, activity) shape, but without column curation. parse_fit_raw returns every message type in the file as its own uncurated DataFrame, in FIT-native units (semicircles, meters, m/s).

TCX & GPX files

TCX and GPX files are parsed natively in this package using lxml. Recognized elements and attributes are mapped onto the same canonical column names as FIT, with the same unit conventions.

The parser supports the following schema versions and extensions:

Unrecognized elements and attributes are exported as string columns named with their XML namespace in Clark notation.

parse_gpx and parse_tcx are the lower-level functions ActivityParser.parse() wraps for these formats. They return the same canonical (records, laps, activity) shape, but without column curation.