Well YARA is good choice to write anti virus/malware signatures in python

https://plusvic.github.io/yara/

http://yara.readthedocs.io/en/v3.4.0/yarapython.html

If you are looking for antivirus tool for windows 

https://www.clamav.net/ is open source ,not sure written in Python

http://www.immunet.com/  is free windows version

Yara is a very popular tool to write signatures for malware files .  Check on github you may find so many yara signatures for different malware families. 

For clamav specific questions , join their mailing list and ask

http://lists.clamav.net/cgi-bin/mailman/listinfo/clamav-users

Now it depends on what your research goals are .  If you can explain your goals i can help u much better. What kind of reliability ? trust you are looking for ? 

Just upload the file to

1. VirusTotal , it uses many commercial engines to let you know if it is malicious or not. 

2. malwr.com , it uses open source cuckoo sandbox and lets you know if it is malicious or not.  https://malwr.com/submission/

In both the cases ( or similar services) , they gives attributes of the file for you to write signatures (using Yara etc.) 

Virus or malware detection is not done with just static analysis both of the above services do dynamic sandboxing of the file as well to observe the run time behaviour. 

Go read about features of https://www.cuckoosandbox.org/ as well 

ask for help on the above mailing list of clamav . you could try cuckoo sandbox too. 

Yes Cuckoo sandbox  is better than Clamav.