Reading_and_Writing_CSV_Files.py

"""
Project for Week 3 of "Python Data Analysis".
Read and write CSV files using a dictionary of dictionaries.

Be sure to read the project description page for further information
about the expected behavior of the program.
"""

import csv

def read_csv_fieldnames(filename, separator, quote):
    """
    Inputs:
      filename  - name of CSV file
      separator - character that separates fields
      quote     - character used to optionally quote fields
    Ouput:
      A list of strings corresponding to the field names in
      the given CSV file.
    """
    with open(filename, "rt", newline='') as csvfile:
        csvreader = csv.DictReader(csvfile,
                                   delimiter=separator, # default ,
                                   quotechar=quote, # default "
                                   quoting=csv.QUOTE_MINIMAL)
    return csvreader.fieldnames


def read_csv_as_list_dict(filename, separator, quote):
    """
    Inputs:
      filename  - name of CSV file
      separator - character that separates fields
      quote     - character used to optionally quote fields
    Output:
      Returns a list of dictionaries where each item in the list
      corresponds to a row in the CSV file.  The dictionaries in the
      list map the field names to the field values for that row.
    """
    table = []
    with open(filename, "rt", newline='') as csvfile:
        csvreader = csv.DictReader(csvfile,
                                   delimiter=separator, # default ,
                                   quotechar=quote, # default "
                                   quoting=csv.QUOTE_MINIMAL)
        for row in csvreader:
            table.append(row)
    return table


def read_csv_as_nested_dict(filename, keyfield, separator, quote):
    """
    Inputs:
      filename  - name of CSV file
      keyfield  - field to use as key for rows
      separator - character that separates fields
      quote     - character used to optionally quote fields
    Output:
      Returns a dictionary of dictionaries where the outer dictionary
      maps the value in the key_field to the corresponding row in the
      CSV file.  The inner dictionaries map the field names to the
      field values for that row.
    """
    table = {}
    with open(filename, "rt", newline='') as csvfile:
        csvreader = csv.DictReader(csvfile,
                                   delimiter=separator, # default ,
                                   quotechar=quote, # default "
                                   quoting=csv.QUOTE_MINIMAL)
        for row in csvreader:
            table[row[keyfield]] = row
    return table


def write_csv_from_list_dict(filename, table, fieldnames, separator, quote):
    """
    Inputs:
      filename   - name of CSV file
      table      - list of dictionaries containing the table to write
      fieldnames - list of strings corresponding to the field names in order
      separator  - character that separates fields
      quote      - character used to optionally quote fields
    Output:
      Writes the table to a CSV file with the name filename, using the
      given fieldnames.  The CSV file should use the given separator and
      quote characters.  All non-numeric fields will be quoted.
    """
    with open(filename, 'w', newline='') as csvfile:
        csv_writer = csv.DictWriter(csvfile,
                                fieldnames=fieldnames,
                                delimiter=separator,
                                quotechar=quote,
                                quoting=csv.QUOTE_NONNUMERIC)
        csv_writer.writeheader()
        for row in table:
            csv_writer.writerow(row)