Merge first worksheet in all Excel workbooks in a folder

Merge_Excel_Workbooks

from xlwings import Workbook, Range
import pandas as pd
import os
import re

# Script to merge a folder containing Excel workbooks into a single workbook.
# The folder should only contain Excel workbooks and must all either be in csv, xls or xlsx format
# To run, open the command prompt and enter the command python Merge_Excel_Workbooks.py

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function to load data into Excel without overloading memory
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def chunk_df(df, sheet, startcell, chunk_size=1000):

    if len(df) <= (chunk_size + 1):
        Range(sheet, startcell, index=False, header=True).value = df

    else:
        Range(sheet, startcell, index=False).value = list(df.columns)
        c = re.match(r"([a-z]+)([0-9]+)", startcell[0] + str(int(startcell[1]) + 1), re.I)
        row = c.group(1)
        col = int(c.group(2))

        for chunk in (df[rw:rw + chunk_size] for rw in
                      range(0, len(df), chunk_size)):
            Range(sheet, row + str(col), index=False, header=False).value = chunk
            col += chunk_size

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Script
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# Prompt to enter the folder path.
# Only Excel Workbooks should be included in the folder path and all should either be in csv, xls or xlsx format
workbook_folder = raw_input('Enter folder path of workbooks to merge: ')
workbook_folder = os.path.normpath(workbook_folder)

passback_templates = os.listdir(workbook_folder)

temp_to_merge = []
for i in passback_templates:
    temp_to_merge.append(workbook_folder + '/' + str(i))

merged_workbooks = pd.DataFrame()

# 0 in the read_excel method refers to the index of the sheet. The first
# sheet in the workbook has a 0 index.
for sheet in temp_to_merge:
    tab = raw_input('Enter worksheet name to merge: ')
    if sheet[:-4] == '.csv':
        workbook = pd.read_csv(sheet, index_col=None, na_values=[0])
        merged_workbooks = merged_workbooks.append(workbook)
    else:
        workbook = pd.read_excel(sheet, tab, index_col=None, na_values=[0])
        merged_workbooks = merged_workbooks.append(workbook)

merged_workbooks.fillna(0, inplace = True)

# A new workbook will open and copy the merged data.
wb = Workbook()

chunk_df(merged_workbooks, 'Sheet1', 'A1')