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Task/Standard-deviation/Python/standard-deviation-1.py

@@ -0,0 +1,22 @@
+>>> from math import sqrt
+>>> def sd(x):
+    sd.sum  += x
+    sd.sum2 += x*x
+    sd.n    += 1.0
+    sum, sum2, n = sd.sum, sd.sum2, sd.n
+    return sqrt(sum2/n - sum*sum/n/n)
+
+>>> sd.sum = sd.sum2 = sd.n = 0
+>>> for value in (2,4,4,4,5,5,7,9):
+    print (value, sd(value))
+
+
+(2, 0.0)
+(4, 1.0)
+(4, 0.94280904158206258)
+(4, 0.8660254037844386)
+(5, 0.97979589711327075)
+(5, 1.0)
+(7, 1.3997084244475311)
+(9, 2.0)
+>>>