cmap=plt.cm.gray, cmap=mpl.cm.binary and cmap=plt.get_cmap("gray")

i just wanted to ask that what is the difference between all these three and the other functions. Please help me out sir I searched a lot on the internet over this issue but could not be resolved.
My issue is that :--
1>Are these three almost same function or are different with different set of color maps?
2>Are the color maps same but perform differently when operated on these three?
3>If not then are these functions some data or dataset specific if not then what are the use of these three statements...
You can understand my breadth of confusion sir please help...