How to parse an HL7 message using python HL7Apy?

Here is my code:

from hl7apy.parser import parse_message

hl7 = open("hl7.txt", "r").read()
msg = parse_message(hl7)
print(msg.children)

result:

[<Segment MSH>]

It shows only the first segment, seems simple but I don't know what i'm doing wrong.

I've tried from a text file, passing the message directly or even with another HL7 message, but always got same results.

Here is the message:

MSH|^~\&|SendingAPP|TEST|||20080617143943||ORU^R01|1|P|2.3.1||||||UNICODE
PID|1||7393670^^^^MR||Joan^JIang||19900804000000|Female
PV1|1||nk^^001
OBR|1||20071207011|00001^Automated Count^99MRC||20080508140600|20080508150616|||John||||20080508150000||||||||||HM||||||||TEST

Here is my message in notepad++ where all characters are shown:

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