can only concatenate str (not "lxml.etree._Element") to str

This error occurs when you are trying to concatenate a string with an object of type "lxml.etree._Element", which is not allowed. To concatenate the object with the string, you need to convert it to a string first. You can use the `str()` function to convert the object to a string. Here's an example:

import lxml.etree as ET

# Assume element is an lxml.etree._Element object
element = ET.Element("tag")

# Convert the element to a string using ET.tostring() method
element_string = ET.tostring(element).decode()

# Concatenate the string with another string
result = "Some text " + element_string
print(result)

In this example, `ET.tostring()` method is used to convert the lxml.etree._Element object `element` to a string. The resulting string `element_string` can then be concatenated with another string using the `+` operator.