def get_valid_varname(varname):
vname = varname<EOL>for s, r in VARNAME_MAP_CHAR:<EOL><INDENT>vname = vname.replace(s, r)<EOL><DEDENT>return vname<EOL>
Replace characters (e.g., ':', '$', '=', '-') of a variable name, which
may cause problems when using with (CF-)netCDF based packages.

Parameters
----------
varname : string
    variable name.

Notes
-----
Characters replacement is based on the table stored in
:attr:`VARNAME_MAP_CHAR`.