Hi everybody I`m using spades trying to assembly a trypanosomatid genome, i just have around 150 MB reads from nanopore sequencer, the smallest read its about 150 bp, and the longest about 84 kb,  I know that i have no enough reads for genome assembly but I am trying to do it anyway, thats my command line:

    spades.py --careful --nanopore --only-assembler -o out_spades -s file.fastq

It does not works, did somebody has used it before? 

Thanks! 
Ok, actually it will only use Nanopore as part of a hybrid assembly. From the docs:

"SPAdes should not be used if only PacBio CLR, Oxford Nanopore, Sanger reads or additional contigs are available."

So it's expecting the nanopore reads filename after the --nanopore argument (which explains your error) but it's also expecting another file to do a hybrid assembly.

Do you have Illumina or other data?