python dictionary keyerror

Handling the KeyError for python dictionary

python dictionary KeyError

The KeyError is quite commonly seen when dealing with the dictionary objects. when trying to access the dictionary while the key does not exists, then this error will be showing up. Usually to avoid this error, we will need to check if the key exists before accessing the value.

For instance, you can check if the key “country” exists in my_dict and then check if the values is “SGP” like the below. But the code does not look elegant.

my_dict = {"name" : "National University of Singapore", "address" : "21 Lower Kent Ridge Rd Singapore", "contact": "68741616"}
if my_dict.get("country") and my_dict["country"] == "SGP":
    print(f"country code is {my_dict['country']}")

You may also see someone uses the below way to make the code more concise. To pass in a default value if the key does not exists:

if my_dict.get("country", "") == "SGP":
    print(f"country code is {my_dict['country']}")

The Zen of Python tells us

Explicit is better than implicit.

So the above code actually does not follow this principal. If you go through the python documentation for dictionary, there is indeed a way to get the value of the key and meanwhile setting a default value if the key is new to the dictionary. Below code shows how it works:

if my_dict.setdefault("country", "") == "SGP":
    print(f"country code is {my_dict['country']}")

By doing the above, the key “country” will be added into the my_dict with a default value if the key does not exists previously, and then return the value of this key.

To extend the above setdefault method, if the value is a list of objects, you can also use this method to initialize it and then set the value.

my_dict.setdefault("faculty", []) # use list or set()
my_dict["faculty"].append("Computer Science")


As per always, welcome for any comments or questions.


openpyxl write excel with styles

Openpyxl library to write excel file with styles

openpyxl to write excel files with styles

Openpyxl probably the most popular python library for read/write Excel xlsx files. In this article, I will be sharing with you how to write data into excel file with some formatting.

Let’s get started with openpyxl.

If you have not yet installed this openpyxl library in your working environment, you may use the below command to install it.

pip install openpyxl

And we shall import the library and modules at the beginning of the script:

import openpyxl
from openpyxl.styles import Alignment, Border, Side, Font

Now I am going to create a new excel with the sheet name as “Demo”:

workbook = openpyxl.Workbook()
sheet =
sheet.title = "Demo"

Assuming if you have the below data that you want to write into the excel file:

raw_data = [["University Name", "No. of Students", "Address", "Contact"],
 ["National University of Singapore", "35908", "21 Lower Kent Ridge Rd, Singapore 119077", "68741616"],
 ["Nanyang Technological University", "31687", "50 Nanyang Ave, 639798", "67911744"],
 ["Singapore Management University", "8182", "81 Victoria St, Singapore 188065", "68280100"]]

You can loop through the list to get the value and assign it to a particular excel cell. Note that the excel row and columns always starts from 1.

for row_idx, rec in enumerate(raw_data):
    for col_idx, val in enumerate(rec):
        sheet.cell(row=row_idx+1, column=col_idx+1).value = val

if you save your data now via the below code, you will see that the saved excel does not come with any formatting (default formatting)"Demo.xlsx")

openpyxl write excel file with styles

As you can see, the format does not look good and some of the column width needs to be adjusted in order to see the full content. Let’s apply some styling to the cells.

Let’s draw the borders for each of the cells, you can specify the color of the border as well as the border style. for more border styles, you can refer to this openpyxl document. you can also use different style for different side of the borders.

thin = Side(border_style="thin", color="303030")
black_border = Border(top=thin, left=thin, right=thin, bottom=thin)

you can also give different width for the different columns as per below :

sheet.column_dimensions["A"].width = 27
sheet.column_dimensions["B"].width = 12
sheet.column_dimensions["C"].width = 33
sheet.column_dimensions["D"].width = 8

Define your own font style:

font = Font(name='Calibri', size=9, bold=True, color='07101c')

Define the alignment style, and you can definitely use different alignment style for different columns. Here I just defined 1 style for all cells.

align = Alignment(horizontal="center", wrap_text= True, vertical="center")

Next, Let’s apply the above styles to each of the cell and save the worksheet:

for label in ["A", "B", "C", "D"]:
    for col_idx in range(row_num):
        idx = label + str(col_idx + 1)
	sheet[idx].alignment = algin
	sheet[idx].font = font
	sheet[idx].border = black_border"Demo.xlsx")

The final output should be similar to the below, which looks much better with the styling.

openpyxl write excel with styles


As per always, welcome to any comments or questions.

python send email from outlook

How to send email from outlook in python

In the previous article, I have explained how to read and save attachments from the outlook by using pywin32 library. In this article, I will walk through with you how to send email from outlook with the same library.


You need to install the pywin32 library in your working environment.

pip install pywin32

and import this library in your script.

import win32com.client

Let’s get started!

You will first need to initiate the outlook application by calling the below:

outlook = win32com.client.Dispatch('outlook.application')

In outlook, email, meeting invite, calendar, appointment etc. are all considered as Item object. Hence we can use the below to create an email object:

mail = outlook.CreateItem(0)

for this mail item, there are various attributes we can set, such as the below To, CC, BCC, Subject, Body, HTMLBody etc. as well as the Attachments:

mail.To = '[email protected]'
mail.Subject = 'Sample Email'
mail.HTMLBody = '<h3>This is HTML Body</h3>'
mail.Body = "This is the normal body"
mail.CC = '[email protected]'

You can add multiple attachments by calling the Attachments.Add multiple times.

Trigger to send out email from outlook

With the above attributes set, you shall be able to send out the email since all the necessary info are provided. Below line of code will trigger to send email from outlook application.


You may also wonder what if you just want to reply to a particular email instead of writing new email? In this case, you will need to find out the email message first and then use the message.Reply() or message.ReplyAll() to reply to the original message. Do check on my this article.


This is just a sample demo of how to send emails, and there are plenty of things you can do with pywin32 library, do check my other related articles, such as this.

Last but not the least, welcome to any comments or questions. Follow me on twitter for more updates.

python read email from outlook and save attachment

How to read email from outlook in python

There are always scenarios that you may wonder how to have a program to automatically read email from outlook and do some processing based on certain criteria. The most common use case is that you want to auto process email attachments when receiving some scheduled reports. In this article, I will be explaining to you how to use python to read email from outlook and save attachment files into the specified folder.


In order to be able to access the outlook native application, we will need to make use of the pywin32 library. Make sure you have installed this library and imported into your script.

import win32com.client
#other libraries to be used in this script
import os
from datetime import datetime, timedelta

Let’s get started!

Like communicating with other system or app, you will need to initiate a session in the first place. By calling the GetNamespace function, you can get the outlook session for the subsequent operations.

outlook = win32com.client.Dispatch('outlook.application')
mapi = outlook.GetNamespace("MAPI")

if you have configured multiple accounts in your outlook, you need to pass in the account name when accessing it’s folders, we can cover this topic in another article. For this article, let assume we only have 1 account configured in outlook.

for account in mapi.Accounts:

To access the inbox folder, you will need to pass in the folder type – 6 in the below function. You may refer to this doc to understand the full list of folder types, such as the draft, outbox, sent, deleted items folder etc.

inbox = mapi.GetDefaultFolder(6)

What if your email is in a sub folder under your inbox? The GetDefaultFolder has the Folders attribute where you can access to the sub folder by it’s name. For instance, to access the “your_sub_folder” under the inbox folder:

inbox = mapi.GetDefaultFolder(6).Folders["your_sub_folder"]

Read email from outlook

Now you are accessible to the inbox and it’s sub folder. You can view all the messages by getting the items as per below. But you may want filter the messages by certain criteria, such as the receiving date, from, subject etc. To do that, we can apply some filter conditions to the messages.

messages = inbox.Items

Use Restrict function to filter your email message. For instance, we can filter by receiving time in past 24 hours, and email sender as “[email protected]” with subject as “Sample Report”

received_dt = - timedelta(days=1)
received_dt = received_dt.strftime('%m/%d/%Y %H:%M %p')
messages = messages.Restrict("[ReceivedTime] >= '" + received_dt + "'")
messages = messages.Restrict("[SenderEmailAddress] = '[email protected]'")
messages = messages.Restrict("[Subject] = 'Sample Report'")

Save attachment files

With all the above filters, we shall only have the messages that we are interested in. Let’s loop through the message and check for the details.

#Let's assume we want to save the email attachment to the below directory
outputDir = r"C:\attachment"
    for message in list(messages):
	    s = message.sender
	    for attachment in message.Attachments:
	        attachment.SaveASFile(os.path.join(outputDir, attachment.FileName))
	        print(f"attachment {attachment.FileName} from {s} saved")
	except Exception as e:
		print("error when saving the attachment:" + str(e))
except Exception as e:
		print("error when processing emails messages:" + str(e))

There are other attributes like Body, Size, Subject, LastModificationTime etc., please check this Microsoft documentation for more details.

If the particular problem you are trying to solve is not covered in this article, you may check my another post 5 Tips For Reading Email From Outlook In Python. And you may be also interested to see how to send email from outlook in python, please check this article.

As per always, welcome any comments or questions. Follow me on twitter for more updates.

Fix the CompDocError when reading excel file with xlrd


You may have seen this CompDocError before if you used python xlrd library to read the older version of the excel file (.xls). When directly opening the same file from Microsoft Excel, it is able to show the data properly without any issue.

This usually happens if the excel file is generated from 3rd party application, the program did not follow strictly on the Microsoft Excel standard format, although the file is readable by Excel but it fails when opening it with xlrd library due to the non-standard format or missing some meta data. As you may have no control on how the 3rd party application generate the file, you will need to find a way to handle this CompDocError in your code.




Option 1:

If you look at the error message, the error raised from  the line 427 in the in your xlrd package. Since you confirm there is no problem with the data in your excel file except the minor format issue, you can open the and comment out the lines for raising CompDocError exception.

while s >= 0:
    if self.seen[s]:
        #print("_locate_stream(%s): seen" % qname, file=self.logfile); dump_list(self.seen, 20, self.logfile)
        #raise CompDocError("%s corruption: seen[%d] == %d" % (qname, s, self.seen[s]))

Option 2:

You may notice if you open your file in Microsoft Excel and save it, you will be able to use xlrd to read and no exception will be raised. This is because Excel already fixed the issues for you when saving the file. You can use the same approach in your code to fix this problem.

To do that, you can use the pywin32 library to open the native Excel application and re-save the file.


import win32com.client as win32

excel_app = win32.Dispatch('Excel.Application')
wb ="test.xls")
excel_app.DisplayAlerts = False #do not show any alert when closing the excel




For option 1, it is good if your program only reads the files generated from the same source. If your program needs to read different excel files from different sources, it may not be a good to always assume the “CompDocError” can be ignored.


For option 2, when calling the excel_app.quit(), the entire Excel application will be closed without any alert. If you have other excel files opening at the time, it will be all closed together. So this solution is good if your program will run in a standalone environment or you confirm no other process/people will be using excel when running your code.


If you would like to understand more about how to read & write excel file with xlrd, please check this article.