Add python-abs.md

python-abs.md

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+# Python abs()
+
+`abs()` is a built in function in Python 3, to compute the absolute value of any number. The argument can even be a [complex number](https://docs.python.org/3.0/library/cmath.html), and in that case its [modulus](http://www.mathcentre.ac.uk/resources/sigma%20complex%20number%20leaflets/sigma-complex9-2009-1.pdf) is returned.
+
+## Argument
+It takes one argument `num` - an integer, or decimal, or a complex number.
+
+## Return Value
+The return value would be a positive number. Even if complex number is passed, it would return its magnitude, computed as per complex number algebra.
+
+## Code Sample
+
+```python
+print(abs(3.4)) # prints 3.4
+print(abs(-6)) # prints 6
+print(abs(3 + 4j)) # prints 5, because |3 + 4j| = 5
+```
+:rocket: [REPL It!](https://repl.it/CL8k/0)