Using Entrez.efetch() to retrive .fasta file from any NCBI database?
In order to download the FASTA sequence of transcript variants using Entrez eutilities, you will have to use Entrez.elink to get a list of transcript accessions for the gene of interest and then use Entrez.efetch to fetch the sequence(s). Just to give you an idea, you can use Entrez Direct for this as follows:
elink -db gene -id 682 -target nuccore -name gene_nuccore_refseqrna \
  | efetch -format fasta

You can find more Entrez Link descriptions here. Note, there is a gene_fasta option for efetch but it still returns only the transcript sequence (i.e., no intron sequence).
If you need the full gene sequence (including the intronic regions), you can use the commands mentioned here.
Alternatively, you can use NCBI Datasets for this. You can use the web interface, command line tool or the python API. This page with the how-to articles has the information you seek.