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IntroToPython

-                      v52
+                      v53
 The solution is [wiki:ProgrammingAnswerPotatoExercise here].   This concludes Lesson 2.
 = Lesson 3:  Functions =
 So are you tired of just printing stuff yet?   In the last lesson, we introduced you to all sort of ways to make decisions and loop over code to make your program easier to read and shorter too.
 …
  * `round(x,[n])`:  Rounds a decimal number x to n digits after the decimal point.  The [] means that the n is optional, if you don't include it, n=0.
  * `sum(iterable)`:  Sums all the numbers in the list ''iterable''.
+ * str.isdigit():   Strings and some other variable types like lists have some special functions just for them, called methods.  This one returns true of all of the digits in the string are numbers, others are [[https://docs.python.org/3/library/stdtypes.html#string-methods|here]].   '123' would return ''True'', "Cat" would return ''False''. Handy for validation
 Here's some examples of how they're used (don't forget to look at earlier lessons for range() and print().
 …
 }}}
+You can combine these functions with control structures to do interesting stuff too:
+{{{
+#!python
+while(!x.isdigit())
+   x=input("Enter x")
+while(!x.isdigit())
+   y=input("Enter y")
+z=pow(x,y)
+if z>100:
+  print("That's-a big number!")
+}}}
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