python - How to overload __init__ method based on argument type? -

-

let's have class has member called data list.

i want able initialize class with, example, filename (which contains data initialize list) or actual list.

what's technique doing this?

do check type looking @ __class__?

is there trick might missing?

i'm used c++ overloading argument type easy.

a neater way 'alternate constructors' use classmethods. instance:

>>> class mydata: ...     def __init__(self, data): ...         "initialize mydata sequence" ...         self.data = data ...      ...     @classmethod ...     def fromfilename(cls, filename): ...         "initialize mydata file" ...         data = open(filename).readlines() ...         return cls(data) ...      ...     @classmethod ...     def fromdict(cls, datadict): ...         "initialize mydata dict's items" ...         return cls(datadict.items()) ...  >>> mydata([1, 2, 3]).data [1, 2, 3] >>> mydata.fromfilename("/tmp/foobar").data ['foo\n', 'bar\n', 'baz\n'] >>> mydata.fromdict({"spam": "ham"}).data [('spam', 'ham')]

the reason it's neater there no doubt type expected, , aren't forced guess @ caller intended datatype gave you. problem isinstance(x, basestring) there no way caller tell you, instance, though type not basestring, should treat string (and not sequence.) , perhaps caller use same type different purposes, single item, , sequence of items. being explicit takes doubt away , leads more robust , clearer code.


Comments

Post a Comment

Popular posts from this blog

c++ - How do I get a multi line tooltip in MFC -

-
right now, have tool tip pops when hover on edit box. problem tool tip contains multiple error messages , in 1 long line. need have each error message on own line. error messages contained in cstring new line seperating them. my existing code below. bool ontooltiptext(uint, nmhdr* pnmhdr, lresult* presult) { assert(pnmhdr->code == ttn_needtexta || pnmhdr->code == ttn_needtextw); // need handle both ansi , unicode versions of message tooltiptexta* pttta = (tooltiptexta*)pnmhdr; tooltiptextw* ptttw = (tooltiptextw*)pnmhdr; // tchar szfulltext[256]; cstring strtiptext=_t(""); uint nid = pnmhdr->idfrom; if (pnmhdr->code == ttn_needtexta && (pttta->uflags & ttf_idishwnd) || pnmhdr->code == ttn_needtextw && (ptttw->uflags & ttf_idishwnd)) { // idfrom hwnd of tool nid = ::getdlgctrlid((hwnd)nid); } //m_errprojaccel[ch] contains 1 or more error messages each...
Read more

asp.net - In javascript how to find the height and width -

-
i having .aspx , masterpage page. in masterpage loading aspx page . in aspx page design using generating table structure using code-behind server in javascript how find height , width . regards, kumar if you're looking table height , width, should it var tbl = document.getelementbyid('tbldemo'); alert(tbl.offsetwidth + '\n' + tbl.offsetheight);
Read more

c# - DataTable to EnumerableRowCollection -

-
i have datatable according client requirement can contain invalid date "00/00/1999",null,empty string.(typed datset) when collect them enumerables wish convert of invalid forms empty string. (i.e) enumerablerowcollection<datarow> query = order in _table.asenumerable() select new { orderdate= string.isnullorempty(convert.tostring(order.field<datetime>("orderdate")) || (how check date invalid date) ? string.empty : order.field<datetime>("orderdate") } how check whether date valid date or not? datetime.tryparse...like given current code: datetime date; enumerablerowcollection<datarow> query = order in _table.asenumerable() select new { orderdate= string.isnullorempty(convert.tostring(order.field<datetime>("orderdate")) || !datetime.tryparse(convert.tostring(order.field<datetime...
Read more