csv_stats.py in Python

Summary statistics for one CSV column, stdlib only.

import csv
import statistics
import sys


def column_stats(path, column):
    with open(path, newline="") as f:
        values = [float(row[column]) for row in csv.DictReader(f)
                  if row.get(column)]
    if not values:
        raise SystemExit(f"no values in column {column!r}")
    return {
        "count": len(values),
        "mean": statistics.mean(values),
        "median": statistics.median(values),
        "stdev": statistics.stdev(values) if len(values) > 1 else 0.0,
    }


def main():
    if len(sys.argv) != 3:
        raise SystemExit(f"usage: {sys.argv[0]} FILE COLUMN")
    path, column = sys.argv[1], sys.argv[2]
    for name, value in column_stats(path, column).items():
        print(f"{name:>8}: {value:.3f}")


if __name__ == "__main__":
    main()

How it works

1. csv.DictReader yields rows as dicts keyed by header.
2. Values parse to float; blanks are skipped.
3. The statistics module supplies mean, median, and stdev.

Keywords and builtins used here

• as
• column_stats
• def
• else
• float
• for
• if
• len
• main
• open
• print
• raise
• return
• with

The run, in numbers

Lines

29

Characters to type

673

Tokens

215

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 117 seconds.

Type this snippet

Step 5 of 5 in Encore, step 72 of 72 in Language basics.

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