Python df.to_excel() storing numbers as text in excel. How to store as Value?

In addition to the other solutions where the string data is converted to numbers when creating or using the dataframe it is also possible to do it using options to the xlsxwriter engine:

writer = pd.ExcelWriter('output.xlsx',
                        engine='xlsxwriter',
                        options={'strings_to_numbers': True})

From the docs:

strings_to_numbers: Enable the worksheet.write() method to convert strings to numbers, where possible, using float() in order to avoid an Excel warning about "Numbers Stored as Text".

Consider converting numeric columns to floats since the pd.read_html reads web data as string types (i.e., objects). But before converting to floats, you need to replace hyphens to NaNs:

import pandas as pd
import numpy as np

dfs = pd.read_html('https://www.google.com/finance?q=NASDAQ%3AGOOGL' +
                   '&fstype=ii&ei=9YBMWIiaLo29e83Rr9AM', flavor='html5lib')
xlWriter = pd.ExcelWriter('Output.xlsx', engine='xlsxwriter')
workbook = xlWriter.book

for i, df in enumerate(dfs):
    for col in df.columns[1:]:                  # UPDATE ONLY NUMERIC COLS 
        df.loc[df[col] == '-', col] = np.nan    # REPLACE HYPHEN WITH NaNs
        df[col] = df[col].astype(float)         # CONVERT TO FLOAT   

    df.to_excel(xlWriter, sheet_name='Sheet{}'.format(i))

xlWriter.save()

That is probably because the Data Types of those columns where the warning is showing are objects and not Numeric Types, such as int or float.

In order to check the Data Types of each column of the DataFrame, use dtypes, such as

print(df.dtypes)

In my case, the column that was stored as object instead of a numeric value, was PRECO_ES

As, in my particular case, the decimal numbers are relevant, I have converted it, using astype, to float, as following

df['PRECO_ES'] = df['PRECO_ES'].astype(float)

If we check again the Data Types, we get the following

Then, all you have to do is export the DataFrame to Excel

#Export the DataFRame (df) to XLS
xlsFile = "Preco20102019.xls"
df.to_excel(xlsFile)

#Export the DataFRame (df) to CSV
csvFile = "Preco20102019.csv"
df.to_csv(csvFile)

If I then open the Excel file, I can see that the warning is not showing anymore, as the values are stored as numeric and not as text