Issue #4869: clarify documentation for random.expovariate.

e6dc5312 · Mark Dickinson · fde5b803 · e6dc5312 · e6dc5312
Kaydet (Commit) e6dc5312 authored Ock 07, 2009 tarafından Mark Dickinson
Hide whitespace changes
Inline Side-by-side

Showing with 10 additions and 6 deletions

random.rst Doc/library/random.rst +5 -3

random.py Lib/random.py +5 -3

No files found.
--- a/Doc/library/random.rst
+++ b/Doc/library/random.rst
@@ -210,9 +210,11 @@ be found in any statistics text.

 .. function:: expovariate(lambd)

-   Exponential distribution.  *lambd* is 1.0 divided by the desired mean.  (The
-   parameter would be called "lambda", but that is a reserved word in Python.)
-   Returned values range from 0 to positive infinity.
+   Exponential distribution.  *lambd* is 1.0 divided by the desired
+   mean.  It should be nonzero.  (The parameter would be called
+   "lambda", but that is a reserved word in Python.)  Returned values
+   range from 0 to positive infinity if *lambd* is positive, and from
+   negative infinity to 0 if *lambd* is negative.


 .. function:: gammavariate(alpha, beta)

--- a/Lib/random.py
+++ b/Lib/random.py
@@ -413,9 +413,11 @@ class Random(_random.Random):
    def expovariate(self, lambd):
        """Exponential distribution.

-        lambd is 1.0 divided by the desired mean.  (The parameter would be
-        called "lambda", but that is a reserved word in Python.)  Returned
-        values range from 0 to positive infinity.
+        lambd is 1.0 divided by the desired mean.  It should be
+        nonzero.  (The parameter would be called "lambda", but that is
+        a reserved word in Python.)  Returned values range from 0 to
+        positive infinity if lambd is positive, and from negative
+        infinity to 0 if lambd is negative.

        """
        # lambd: rate lambd = 1/mean