[Biopython] MUSCLE for alignment

[=?GB2312?B?wdbQ0Nba?=]

Hi all !
I have a seqdump.fasta file:
>lcl|24977
TGAGAAAGACTTGAGAGGACA

>lcl|24977:8-21
GAGATGACTTAGAGGACA

I want to use a wrapper for Muscle in Biopython to align the two seq.
the alignment result will put into a existing fasta file.

>>>from Bio.Align.Applications import MuscleCommandline
>>>mcline = MuscleCommandline(input='seqdump.fasta',out='result.fasta')

But i can not find anything in the result.fasta after i run the command.
Do i have any missing to get the result?

regards
Lin