Python sendgrid - Concat/Add a string to HTML_CONTENT

i Am trying to add a string to thml content and out that i am getting is not as required
'str1' should be added in place of str1 to 'Attached is the report of your data - +str1'

str1= 'StringToBeAdded'
html_content1 = ''' Hi All,
        <br>
        <br>
        Greetings from xyz!
        <br>
        Attached is the report of your data - + str1
        <br>
        <br>
        Note: This is an automated email. In case of any queries, please reach us at 
        <br>
        Regards,
        <br>
        abc '''
message = Mail(
    from_email='from@example.com',
    to_emails=to@example.com',
    subject='Mail,
    html_content=html_content1)

Expected Output

Attached is the report of your data - StringToBeAdded

Thanks in advance

You need to properly quote, see below such that str1 is treated as a variable , your post shows it within ''' such that it will not be interpreted as a variable merely as text.

str1= 'StringToBeAdded'
html_content1 = ''' Hi All,
            <br>
            <br>
            Greetings from xyz!
            <br>
            Attached is the report of your data - ''' + str1 + ''' 
            <br>
            <br>
            Note: This is an automated email. In case of any queries, please reach us at
            <br>
            Regards,
            <br>
            abc '''