Reset file object position in is_png()

[chunan]

Otherwise chunk() function will miss the first 8 bytes when png is file-object-like.

[eight04]

Good catch. However bytes object is not handled correctly. Please use something like:

if isinstance(png, str):
	...
elif hasattr(png, "read"):
	...
elif isinstance(png, bytes):
	png_header = png[:8]
else:
	raise TypeError("Muse be file, bytes, or str")

Also no need to slice it again:

return png_header == PNG_SIGN

[chunan]

Done.

[chunan]

Updated as requested. PTAL.

[eight04]

👍 I'll write some tests before releasing it.