Write byte strings to a file - lxml

Question

I have following code
from lxml import etree
xmlns = "http://www.fpml.org/FpML-5/confirmation"
xsi = "http://www.w3.org/2001/XMLSchema-instance"
fpmlVersion="http://www.fpml.org/FpML-5/confirmation ../../fpml-main-5-6.xsd http://www.w3.org/2000/09/xmldsig# ../../xmldsig-core-schema.xsd"
page = etree.Element("{"+xmlns+"}dataDocument",nsmap={None:xmlns,'xsi':xsi })
doc = etree.ElementTree(page)
page.set("fpmlVersion", fpmlVersion)
trade = etree.SubElement(page,'trade')
party = etree.SubElement(page,'party',id='party1')
partyID = etree.SubElement(party,'partyID')
partyID.text = 'PARTYAUS33'
partyName = etree.SubElement(party,'partyName')
partyName.text = 'Party A'
party = etree.SubElement(page,'party',id='party2')
partyID = etree.SubElement(party,'partyID')
partyID.text = 'BARCGB2L'
partyName = etree.SubElement(party,'partyName')
partyName.text = 'Party B'
s = etree.tostring(doc, xml_declaration=True,encoding="UTF-8",pretty_print=True)
print (s)
How do i save the contents of S to a file

Answer 1

You have to open() a new file in binary mode, and later use the filehandle write() function, so add:
import sys
fd = open(sys.argv[1], 'wb')
at the beginning.
And:
fd.write(s)
at the end.
So, you now have to pass an additional argument to the script, that will be the output file to write. Also note that I use the w flag in the open() function that will destroy (to re-create) any file with that name in current directory.
Run it like:
python3 script.py outfile
That yields:
<?xml version='1.0' encoding='UTF-8'?>
<dataDocument xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.fpml.org/FpML-5/confirmation" fpmlVersion="http://www.fpml.org/FpML-5/confirmation ../../fpml-main-5-6.xsd http://www.w3.org/2000/09/xmldsig# ../../xmldsig-core-schema.xsd">
<trade/>
<party id="party1">
<partyID>PARTYAUS33</partyID>
<partyName>Party A</partyName>
</party>
<party id="party2">
<partyID>BARCGB2L</partyID>
<partyName>Party B</partyName>
</party>
</dataDocument>