change_fasta_header.py

with open ("C:/Users/Tang Ming/Desktop/anotation.txt", "r") as annotation:
    anotation_dict = {}
    for line in annotation:
        line = line.split()
        if line: #test whether it is an empty line
            anotation_dict[line[0]]=line[1:]
        else:
            continue

# really should not parse the fasta file by myself. there are
# many parsers already there. you can use module from Biopython
ofile = open ("C:/Users/Tang Ming/Desktop/output.txt", "w")

with open ("C:/Users/Tang Ming/Desktop/my_fasta.txt", "r") as myfasta:
    for line in myfasta:
        if line.startswith (">"):
            line = line[1:] # skip the ">" character
            line = line.split()
            if line[0] in anotation_dict:
                new_line = ">" + str(line[0]) + " " + " ".join(anotation_dict[line[0]])
                ofile.write ( new_line + "\n")
            else:
                ofile.write ( ">"+ "".join(line) + "\n")
        else:
            ofile.write(line +"\n")


ofile.close() # always remember to close the file.

it seems somewhere messed up at the "\n", some sequences got multiple lines while the others are not.

yes, the last line should add a new line "\n", I though I caught that and made changes. anyways, I updated the code. Thank you!