text: import openpyxl
  import pandas as pd
  import matplotlib.pyplot as plt
  
  def verify_worksheet(file, sheet_name):
      workbook = openpyxl.load_workbook(file)
      try:
          worksheet = workbook[sheet_name]
      except KeyError:
          print("The sheet '{}' does not exist in your file'{}'.".format(sheet_name, file))
  
  def replace_nulls(df):
      NaN = float("NaN")
      missingdata = ["null", "Null", "NULL", "."] # "", " ",
      for item in missingdata:
          df.replace(item, NaN, inplace=True)
  
      df.dropna(axis=0, how= 'all', thresh=None, subset=None, inplace=True) # Delete rows, where every value is null
  
  def sum_features_per_software(df, min_features):
      counts = df.count(axis=1, numeric_only=True) # Count all nonmissing numeric feautures
      sums = df.sum(axis=1, skipna=True, numeric_only=True, min_count=min_features)
      df = df.assign(total_features=counts, number_of_features=sums) # Create new variables
      df = df.assign(percent_of_features=(df['number_of_features']/df['total_features']))
      df['percent_of_features'] = df['percent_of_features'].round(2) # Round percentages
      return df
  
  def keep_top_software(df, variablename, count):
      # variablename: column to sort values by
      # count: number of software tools to keep
      df = df.sort_values(variablename, ascending=False)
      df = df.head(count).reset_index()
      del df['index']
      return df
  