Mosab Ibrahim

Site Reliability Engineer @ GoCardless

Reading Data from Excel Sheets in Python

On May 22nd 2012 I was approached by the official campaign of the presidential candidate "Abolfotoh".

They needed help setting up a Google App Engine application.

It was an interactive map that uses Google Maps to plot data about voters and polling stations.

What they wanted further was to create another application to collect data from their official representatives on the ground and use this tool to feed the Google App Engine application with data.

The application was originally created by "Espace" -an awesome Egyptian company- and published on Google Code.

I helped the official campaign with the setup on Google App Engine, but that is another story.

Before running the project in production, we needed to import a lot of data about the polling stations and the voters, like the Governorate it belonged to, the city, the number of voters per every station, the police station it belongs to, address, etc.

This data was only available in an excel sheet so I had to find a quick programmatic way to import it.

For the sake of simplicity, lets assume the data in the excel sheet was formatted like this :

+-------------------+------------+------------------------+ | Polling
Station   | City       | Total Number of Voters |
+-------------------+------------+------------------------+ | polling_station_1
| Cairo      | 7734                   |
+-------------------+------------+------------------------+ | polling_station_2
| Giza       | 13332                  |
+-------------------+------------+------------------------+ | polling_station_3
| Alexandria | 10901                  |
+-------------------+------------+------------------------+

As in most spreadsheets, the first row is the header row that describes the data, and the actual data is in the rows to follow.

I did a quick search and found several libraries that deal with excel in Python, there is even a website dedicated to listing them http://www.python-excel.org. I chose to go with XLRD, and you can find it in PyPi as well.

We need to install it first by running this command :

$ pip install xlrd

Or

$ easy_install xlrd

Let's start coding.

XLRD calls the whole excel document a "Workbook", to open it we can do the following in an interactive python shell from the same path as the file:

>>> from xlrd import open_workbook book = open_workbook('data.xls')

Now we can manipulate the excel document using this "book" object we created. Remember the book has all the document.

An excel document can have one or multiple sheets inside it that hold the data.

The first sheet has an index of 0, the second has an index of 1 and so on.

To open the first sheet which holds the sample data above we do this:

>>> first_sheet = book.sheet_by_index(0)

Now we are ready to manipulate the sheet, get information about it and extract data from it.

For example to know the number of "effective columns" in the sheet we can print the ncols attribute of the sheet, or to know the number of "effective rows", the rows that contain data, we can use the nrows attribute.

>>> print first_sheet.ncols
3
>>> print first_sheet.nrows
4

We now know how many rows contain actual data in the first sheet of our excel document. Time to loop over the rows and extract data.

>>> for i in range(1, first_sheet.nrows):
      row = first_sheet.row_slice(i)
      station = row[0].value        \
      city = row[1].value
      voters = row[2].value
      print "Polling Station :{} in {} has {} voter".format(station, city, voters)
Polling station polling_station_1 in Cairo has 7734.0 voters
Polling station polling_station_2 in Giza has 13332.0 voters
Polling station polling_station_3 in Alexandria has 10901.0 voters

In the previous snippet of code we started to loop over the rows skipping the first row range(1, first_sheet.nrows)

Then we sliced every row out of the sheet with row_slice() and then accessed it by column index to extract data from columns row[], and then we accessed the value of the cell by calling the row[].value.

This is a very simple usage of the library, I suggest you read its documentation, you will find many great stuff :

>>> import xlrd help(xlrd) help(xlrd.sheet)

Finally check my answer on a question about the issue on StackOverflow.

That's it for now!

 

Category: posts
Tags: Python XLRD Excel