Minor updates to contours_sample_v0.7.py

[cclauss]

• Used print as a function to ease future transition to Python3
• Avoid backslash line continuation (https://www.python.org/dev/peps/pep-0008/#maximum-line-length). A space character inserted to the right of the backslash will be difficult to spot but it change the meaning of the code.
• Use str.format() in place of complex string concatenation
• Question on the four corners of contour