import sys
import re

f1=open(sys.argv[1]).readlines()   #strain distance
f2=open(sys.argv[2]).readlines()   #distance <= 12 strain list
f3=open("rough_transmission_chain","a")

sum_chain_list=[i.rstrip().split()[0] for i in f1 if int(i.rstrip().split()[1])<=12]


def find_transmission_strain(strain):
        cycle_strain = []
        match_strain = []
        True_strain = [i for i in sum_chain_list if i.startswith(strain + "VS") or i.endswith("VS" + strain)]   
        for item in True_strain:
                temp = re.sub("VS", "", item)
                sum_chain_list.remove(item)                     
                if temp[:len(strain)] == strain:
                        match_strain.append(temp[len(strain):])
                        cycle_strain.append(temp[len(strain):])
                else:
                        match_strain.append(temp[0:len(temp) - len(strain)])
                        cycle_strain.append(temp[0:len(temp) - len(strain)])
        if len(cycle_strain) > 0:
                for a in range(len(cycle_strain)):
                        for b in range(len(cycle_strain)):
                                try:
                                        sum_chain_list.remove(cycle_strain[a] + "VS" + cycle_strain[b])
                                except ValueError as e:
                                        pass
                for i in cycle_strain:
                        match_strain.extend(find_transmission_strain(i))                  
        return set(match_strain)


# A will be included in a transmission chain B if distance bewteen A and (any strain in B) is <=12
temp = []

for i in f2:
        i = i.rstrip()
if i not in temp:
        a = list(find_transmission_strain(i))
        a.append(i)
        temp.extend(a)
        for strain in a:
                f3.write(strain + "\t")
        f3.write("\n")

else:
        pass

根据结核菌12SNP的阈值判断传播链