Track my weight using Python

Last updated on 2022-10-13 Tagged under  #python   #programming 

I maintain a text file that serves as my "daily log" where I enter various things: observations, things I track over time, things to do, mini HOWTOs, etc.

One item of interest I've been recording is my weight. Each entry includes the date, a :weight: tag, and the measurement (in kg).

A sample entry looks like ...

2022-07-08T07:19
:weight: 72.1

After several years of weigh-ins and recordings, I've accumulated 1,200+ data points. How can I retrieve these measurements that are mixed in with all other sorts of data?

Enter the power of Python!

I divide this challenge into two parts: 1. Create a Python module (tracktivity) with functions to track any sort of activity (not just weight) in my daily log, and 2. write the actual weight tracking program itself (track_weight.py).

Tracktivity

I make use of Python regular expressions to scan a text file for matching date and value regex patterns of interest, and create a dictionary of the dates and values found as key-value pairs. I can choose to display the results as a dictionary, formatted into columns with summary, or as a scatter plot graph courtesy of plotly.express.

Module re is included in Python. Install plotly via pip ...

$ pip install plotly

Import the necessary modules ...

import re
import plotly.express as px

Function date_value_dict scans a text file for date regex with a corresponding value regex match, and returns a dictionary of dates and values as key-value pairs ...

def date_value_dict(textfile, date_regex, value_regex, value_matchgroup=0):
    dates_values = {}

    with open(textfile) as file_obj:
        current_date = ""  # most recent date match
        for line in file_obj:
            if date := re.search(date_regex, line):
                current_date = date.group()
            if value := re.search(value_regex, line):
                try:
                    value = float(value.group(value_matchgroup))
                except ValueError:
                    value = value.group(value_matchgroup)
                dates_values[current_date] = value
    return dates_values

Function date_value_columns takes a dictionary and returns a list of tuples (formatted using a template), each containing (item number, date string, value) ...

def date_value_columns(dictionary, template):
    dates_values = [template.format(i, k, v) for i, (k, v) in enumerate(dictionary.items())]
    return dates_values

Function date_value_summary takes a dictionary of dates and values, and returns a list summary ...

def date_value_summary(dictionary):
    dct = dictionary
    items = len(dct)
    summary = [
        f"\nLatest:\t{next(iter(dct.items()))[1]}\t(recorded on {next(iter(dct.items()))[0]})",
        f"High:\t{max(dct.values())}\t(recorded on {max(dct, key=dct.get)})",
        f"Low:\t{min(dct.values())}\t(recorded on {min(dct, key=dct.get)})",
        f"Mean:\t{(sum(dct.values()) / items):.1f}\t(calculated from {items} total items)",
    ]
    return summary

Function date_value_scatterplot takes a dictionary of dates and values as key-value pairs, and returns a scatter plot graph with title and label for dates (x-axis) and values (y-axis) ...

def date_value_scatterplot(dictionary, title, label="Values"):
    x_dates = list(dictionary.keys())
    y_values = list(dictionary.values())
    x_dates.reverse()
    y_values.reverse()

    fig = px.scatter(x=x_dates, y=y_values, title=title, labels={"x": "Dates", "y": label})
    fig.show()

track_weight.py

I create track_weight.py that uses the tracking functions from the tracktivity module to scan my daily log for weight measurements and dates recorded, for the purpose of tracking my weight over time.

With the Python module argparse, I can add command-line options to my program ...

#!/usr/bin/env python3
import argparse
import tracktivity as track

Function get_args collects the command-line arguments: -h and --help for a description of the program; -r and --results to display output as a dictionary, as neatly formatted columns, or a scatterplot opened in a web browser (default is columns if no argument provided) ...

def get_args():
    parser = argparse.ArgumentParser(
        description="""
        Scan my daily log for weight measurements and dates recorded for the purpose of tracking my weight over time.
        """,
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
    )
    parser.add_argument(
        "-r",
        "--results",
        metavar="type",
        type=str,
        choices=["dictionary", "columns"],
        default="columns",
        help="Display results as: dictionary, columns",
    )
    return parser.parse_args()

Variables ...

args = get_args()
results = args.results
logfile = "/home/dwa/doc/wiki/index.wiki"  # data source
date = r"^20\d\d-\d\d-\d\d"  # find date pattern at beginning of line
value = r"^(:weight:)\s(\d\d.\d)"  # parentheses create groups in the regex for the group() match obj method
matchgroup = 2  # part of value, enclosed in parentheses, to match; 0 = match entire regex
title = "Track Weight (kg)"
label = "kg"
template = "{0:5}  {1:11} {2:4}"  # three-column layout with padding

Create the dictionary of dates and weights ...

dates_values = track.date_value_dict(logfile, date, value, matchgroup)

Choose how to display the results ...

if results == "dictionary":
    print(dates_values)
elif results == "scatterplot":
    track.date_value_scatterplot(dates_values, title, label)
elif results == "columns":
    print(f"\n{title}\n" + "-" * len(title) + "\n" + template.format("Items", "Dates", "Values"))
    print("\n".join(track.date_value_columns(dates_values, template)))
    print("\n".join(track.date_value_summary(dates_values)))

Now, if I run track_weight.py with --results dictionary I get all my weigh-in measurements and the dates they were recorded as a Python dictionary ...

$ track_weight.py --results dictionary
{'2022-07-08': 72.1, '2022-07-04': 72.1, '2022-07-01': 71.4, ...}

With the data stored in a dictionary, its easy to use it in other functions that can work with and present the data in different ways.

Here I arrange the data into columns (the default), with a summary at the end ...

$ track_weight.py

Track Weight (kg)
-----------------
Items  Dates       Values
    0  2022-07-08  72.1
    1  2022-07-04  72.1

[...]

 1232  2014-01-19  77.6
 1233  2014-01-12  79.8

Latest:	72.1	(recorded on 2022-07-08)
High:	79.8	(recorded on 2014-01-12)
Low:	59.8	(recorded on 2014-12-12)
Mean:	66.9	(calculated from 1234 total items)

To better appreciate the changes over time, its helpful to visualize the data as a scatter plot ...

$ track_weight.py -r scatterplot

A graph is generated by plotly.express, and fig.show() opens an interactive graph in a web browser ...

scatterplot

I really enjoyed putting this together as my first Python data analysis project. Working on a project of personal interest, something that you regularly use, is the very best way to learn how to program (or anything for that matter)!

Sources: track_weight.py and tracktivity

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