A First Taste of `pathlib`¶

May 21, 2019

Introduction¶

The library pathlib is introduced in Python 3.4 and it brings us a spate of convenient features. I try using this library instead of the traditional functions provided in modules os and os.path in one of my projects and demonstrate why it is better than the traditional functions. The task here is to write a function to download the daily volume file from this page for a given year.

Traditional Python Code¶

import requests
import os

def download_file_1(year):
    site_url = 'http://markets.cboe.com/us/equities'
    base_url = f'{site_url}/market_statistics/historical_market_volume'
    url = f'{base_url}/market_history_{year}.csv-dl'

    fpath = os.path.join(os.path.expanduser("~"), 'data', 'daily_volume')
    if not os.path.exists(fpath): os.makedirs(fpath)
    fname = os.path.join(fpath, f'daily_volume_{year}.csv')

    res = requests.get(url)
    with open(fname, 'w') as f:
        f.write(res.text)

if __name__ == "__main__":
    download_file_1(2019)

Using `pathlib`¶

import requests
from pathlib import Path

def download_file_2(year):
    site_url = 'http://markets.cboe.com/us/equities'
    base_url = f'{site_url}/market_statistics/historical_market_volume'
    url = f'{base_url}/market_history_{year}.csv-dl'

    fpath = Path.home().joinpath('data', 'daily_volume')
    fpath.mkdir(parents=True, exist_ok=True)
    fname = fpath / f'daily_volume_{year}.csv'

    res = requests.get(url)
    with fname.open('w') as f:
        f.write(res.text)

if __name__ == "__main__":
    download_file_2(2019)

Main Differences¶

The main differences are highlighted at lines 9, 10, 11 and 14.

Get home directory
- os.path.expanduser("~")
- Path.home()
Join path
- os.path.join('dir', 'subdir')
- Path.joinpath('dir', 'subdir')
Create path
- if not os.path.exists(fpath): os.makedirs(fpath)
- fpath.mkdir(parents=True, exist_ok=True)
Open file
- with open(fname, 'w') as f
- with fname.open('w') as f

Summary¶

pathlib library puts these methods that used to be in os and os.path into a single library and makes it easier to use. For additional features provided by this library, see pathlib.

A First Taste of pathlib¶