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Read and write files safely; parse JSON, CSV, and common text formats.

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Join two CSV files on shared key column in Python

Merge rows from two CSV files by a common key column, outputting combined records to a new file.

csv join dictreader
Python 
import csv

def join_csv(file1, file2, key, output="joined.csv"):
    # Read first CSV into dict keyed by the join column
    with open(file1, newline="") as f1:
        reader1 = csv.DictReader(f1)
        data1 = {row[key]: row for row in reader1}

    # Read second CSV and merge matching rows
    with open(file2, n…
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