Python Function read excel / csv files from a given directory and its subdirectories

5 minute read


The code for the function is as shown below:

import os
import pandas as pd
import numpy as np
from datetime import datetime 

def extract_data(directory_path, columns_to_extract, date_columns=[], rows_to_skip=0, output_filename='output.csv'):
    Extracts data from all Excel and CSV files in the specified directory and its subdirectories that contain all the
    specified columns.

    :param directory_path: The path to the directory to search for Excel and CSV files.
    :param columns_to_extract: A list of column names to extract from each file.
    :param date_columns: A list of column names to parse as dates using pd.to_datetime().
    :param output_filename: The path and filename to save the extracted data in a csv
    :return: A DataFrame containing the extracted data from all Excel and CSV files that contain the specified columns,
    or None if no files contain the specified columns.
    start_time =
    extracted_data = pd.DataFrame()
    files_with_no_columns = []
    sheet_read = ''
    extracted_columns = columns_to_extract.copy()
    extracted_columns.extend(['File Name','SubDir','CreatedDate','LastModifiedDate'])

    for root, dirs, files in os.walk(directory_path):
        for file in files:
            print('Started reading ' + file + ' at: {}'.format( + ' ...')
            if file.endswith('.xlsx') or file.endswith('.xls') or file.endswith('.csv'):
                file_path = os.path.join(root, file)
                columns_found_outer = False
                if file.endswith('.csv'):
                    df = pd.read_csv(file_path,skiprows=rows_to_skip)
                    for col in columns_to_extract:
                        if col in df.columns:
                            columns_found_outer = True
                            #print(col + 'in csv true loop')
                            columns_found_outer = False
                            #print(col + 'in false loop')
                    dfs = pd.read_excel(file_path, sheet_name=None,skiprows=rows_to_skip)
                    for key in dfs.keys():
                        columns_found = False
                        for col in columns_to_extract:
                            if col in dfs[key].columns:
                                columns_found = True
                                #print(col + 'in true loop')
                                columns_found = False
                                #print(col + 'in false loop')
                        if columns_found:
                            columns_found_outer = True
                            df = dfs[key]
                            sheet_read = key
                if columns_found_outer:
                    if len(date_columns) > 0:
                        for col in date_columns:
                            if col in df.columns:
                                df[col] = pd.to_datetime(df[col])
                    df['File Name'] = file
                    df['SubDir'] = os.path.basename(root)

                    createx = modx = os.path.getctime(file_path)
                    xcreate = datetime.fromtimestamp(modx)
                    df['CreatedDate'] = xcreate

                    modx = os.path.getmtime(file_path)
                    xmod = datetime.fromtimestamp(modx)
                    df['LastModifiedDate'] = xmod
                    extracted_data = pd.concat([extracted_data, df[extracted_columns]], ignore_index=True)
                    if file.endswith('.csv'):
                        print(file + ' has been read')
                        print(file + ' has been read and it was last modified on ' + xmod.strftime('%Y-%m-%d') + '. The name of the sheet that was read is: ' + sheet_read)
    if len(files_with_no_columns) > 0:
        print("The following files do not contain the specified columns:")
        for file_path in files_with_no_columns:
    if not extracted_data.empty:
        extracted_data = extracted_data.applymap(lambda s: s.upper() if type(s) == str else s).fillna('')
        print('Started at: {}'.format(start_time) + '. \nEnded at: {}'.format( + '. \nTime elapsed ( {}'.format( - start_time))
        return extracted_data
        print("Specified columns do not exist in any file in the provided directory.")
        print('Started at: {}'.format(start_time) + '. \nEnded at: {}'.format( + '. \nTime elapsed ( {}'.format( - start_time))
        return None


  1. The function extract_data takes in the following parameters:

    • directory_path: the path to the directory to search for Excel and CSV files
    • columns_to_extract: a list of column names to extract from each file
    • date_columns: a list of column names to parse as dates using pd.to_datetime()
    • rows_to_skip: the number of rows to skip when reading each file
    • output_filename: the path and filename to save the extracted data in a CSV file
  2. The function starts by creating an empty DataFrame called extracted_data.

  3. It also initializes variables files_with_no_columns and sheet_read to track files that do not contain the specified columns and to keep track of the current sheet being read when extracting data from Excel files.

  4. The list extracted_columns is created by copying the input columns_to_extract list and adding additional columns for the filename, subdirectory name, file creation date, and last modified date.

  5. The function then loops through all the files in the specified directory and its subdirectories using os.walk().

  6. For each file, it checks if it has a “.xlsx”, “.xls”, or “.csv” extension.

  7. If the file is a CSV file, the function reads it into a DataFrame using pd.read_csv(), skipping the number of rows specified by rows_to_skip.

  8. It then checks if all the columns in columns_to_extract are present in the DataFrame. If so, it sets columns_found_outer to True and proceeds to the next step. If not, it sets columns_found_outer to False and moves on to the next file.

  9. If the file is an Excel file, the function reads all sheets in the file into a dictionary of DataFrames using pd.read_excel() and sheet_name=None. It then loops through all the sheets and all the columns in columns_to_extract, checking if each column is present in each sheet’s DataFrame. If all the columns are present in a sheet, it sets columns_found to True and proceeds to the next step. If not, it sets columns_found to False and moves on to the next sheet in the same Excel file. If at least one sheet contains all the specified columns, the function combines the DataFrames of all sheets into one using pd.concat().

  10. If columns_found_outer is True, it extracts the filename, subdirectory name, file creation date, and last modified date using os.path.basename(), os.path.getctime(), and os.path.getmtime(), and adds them as new columns to the DataFrame. It then appends the DataFrame to the extracted_data DataFrame.

  11. If columns_found_outer is False, it increments the files_with_no_columns counter and prints a warning message.

  12. Finally, the function checks if any files contained the specified columns. If not, it returns None. Otherwise, it sorts the extracted_data DataFrame by filename and saves it to a CSV file using to_csv(). It then prints the number of files processed, the number of files that did not contain the specified columns, and the path to the output file.

Sample Usage

The function can be called in python as shown below:

# set directory path
directory_path = './Work' # Path for the directory where all the files containing data for  extraction are to be searched

# set the columns you want to extract
columns_to_extract = ['Region','Country', 'Product Number','Quantity','Date of Sale']
date_col = ['Date of Sale']
# set the rows to skip
skiprows = 0 #this basically will be number of rows in begining of the files which must be skipped to reach the header row of the data
output_filename = 'Regional Sales Data.csv'
#Call function
df = extract_data(directory_path,columns_to_extract,date_col,skiprows,output_filename)

Now, assuming there were 12 separate files for past 12 months inside the folder then so long as all those files, irrespective of whether they are csv or excel, have the columns Region,Country, Product Number,Quantity,Date of Sale; the function will read the files and extract the data and return it to the dataframe df.

GUI Implementation

A very basic GUI implementation of above function using PySimpleGUI with all codeis available here


The script can directly be copied to a Jupyter cell or can be run from terminal. Following command should ensure all dependencies are installed:

py -m pip install pandas, numpy, pysimplegui

Some things the GUI takes care of are:

  • Allows selection of columns to be extracted from a sample .csv file
  • Allows user to specify which of the selected columns should be parsed as date
  • Gives a date based filename to output
  • Shows colour coded log for which files were read in green and which were ignored in red background.


Some screenshots of the resulting app are as shown below:

Empty Form


Filled Form


Displays extracted output


Displays filename of the output and location where it is saved


Colour coded log



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