Following on your last post, your initial file test.txt looks like that:

WP_XXXXXXXX2.1  PF06325 Ribosomal protein L11 methyltransferase (PrmA)  5
WP_192XXXXXX.1  PF13489 Methyltransferase domain    4
XXXXXXX45.1 PF02310 B12 binding domain  12
XXXXXXX45.1 PF04055 Radical SAM superfamily 5
WP_XXXXXXX29.1  PF13489 Methyltransferase domain    4
WP_0XXXXXXXX.1  PF13489 Methyltransferase domain    4
WP_XXXXXXX90.1  PF06325 Ribosomal protein L11 methyltransferase (PrmA)  5
WP_XXXXXXX90.1  PF06325 Ribosomal protein L11 methyltransferase (PrmA)  7
WP_0XXXXXX62.1  PF13489 Methyltransferase domain    4

And you have another file order.txt that contains your ordered IDs:

XXXXXXX45.1
YP_343434.1
WP_XXXXXXXX2.1
WP_XXXXXXX90.1
WP_0XXXXXX62.1
XP_222222222.2
WP_192XXXXXX.1
WP_XXXXXXX29.1
WP_0XXXXXXXX.1

Since you want to merge by the first field in test.txt and sort them according to order.txt, you have to read first both of the files:

# read 'test.txt'
with open("test.txt",'r') as rf:
    l = rf.readlines()

# read sorted IDs 'order.txt'
with open("order.txt",'r') as rf:
    l_order = rf.readlines()

# remove newlines from each element in list
l_order = [i.strip() for i in l_order]

My previous answers describe how we obtain the merged fields in the file, so I will not go over it again. Since we need to sort the dictionary according to the list, we simply have to do:

# for each element in ordered list
for i in l_order:
    if i in dict_id.keys():                        # if element is in my dictionary's keys
        print(i + "\t" + "; ".join(dict_id[i]))    # print the key and the value
    else:
        print(I)                                   # else prints the element

This should print:

XXXXXXX45.1     PF02310 B12 binding domain      12; PF04055     Radical SAM superfamily 5
YP_343434.1
WP_XXXXXXXX2.1  PF06325 Ribosomal protein L11 methyltransferase (PrmA)  5
WP_XXXXXXX90.1  PF06325 Ribosomal protein L11 methyltransferase (PrmA)  5; PF06325      Ribosomal protein L11 methyltransferase (PrmA)  7
WP_0XXXXXX62.1  PF13489 Methyltransferase domain        4
XP_222222222.2
WP_192XXXXXX.1  PF13489 Methyltransferase domain        4
WP_XXXXXXX29.1  PF13489 Methyltransferase domain        4
WP_0XXXXXXXX.1  PF13489 Methyltransferase domain        4

Full code:

with open("test.txt",'r') as rf:
    l = rf.readlines()

with open("order.txt",'r') as rf:
    l_order = rf.readlines()

l_order = [i.strip() for i in l_order]

dict_id = {}
for i in l:
    key_id = i.split("\t")[0]
    if key_id not in dict_id.keys():
        value = "\t".join(i.split("\t")[1:]).rstrip()
        dict_id[key_id] = [value] 
    else:
        dict_id[key_id].append("\t".join(i.split("\t")[1:]).rstrip())

for i in l_order:
    if i in dict_id.keys():
        print(i + "\t" + "; ".join(dict_id[i]))
    else:
        print(i)

PS: please for further pure programming questions, do post your questions in StackOverflow instead of Bioinformatics.