How can I pass an empty string into triple quoted f-string in Python?

Question

Here is a function using a triple quoted f-string with lots of sub-elements:

def pass_empty_string(param):
    from lxml import etree
    xml = etree.XML(f'''
    <root>
        <child>text</child>
        <child>{param}</child>
        ...
    </root>''')
    return xml

Is it possible to get an empty </child> element when param is getting None or '' value?

Answer 1

You can accomplish this with or:

f"<child>{param or ''}</child>"

Anything in the braces is evaluated as an expression, so...

>>> param = None
>>> f"<child>{param or ''}</child>"
'<child></child>'
>>> param = ''
>>> f"<child>{param or ''}</child>"
'<child></child>'
>>> param = "some valid child"
>>> f"<child>{param or ''}</child>"
'<child>some valid child</child>'

Both '' and None are falsy values, so it will fall back to the RHS of the or, which will be just an empty string.