python-checkins at python
Nov 24, 2009, 8:20 AM
Post #1 of 1
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r76489 - in python/trunk/Doc: faq/design.rst library/decimal.rst library/math.rst library/sqlite3.rst library/turtle.rst tutorial/floatingpoint.rst tutorial/inputoutput.rst tutorial/stdlib2.rst
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Author: mark.dickinson
Date: Tue Nov 24 15:27:02 2009
New Revision: 76489
Log:
Fix some documentation examples involving the repr of a float.
Modified:
python/trunk/Doc/faq/design.rst
python/trunk/Doc/library/decimal.rst
python/trunk/Doc/library/math.rst
python/trunk/Doc/library/sqlite3.rst
python/trunk/Doc/library/turtle.rst
python/trunk/Doc/tutorial/floatingpoint.rst
python/trunk/Doc/tutorial/inputoutput.rst
python/trunk/Doc/tutorial/stdlib2.rst
Modified: python/trunk/Doc/faq/design.rst
==============================================================================
--- python/trunk/Doc/faq/design.rst (original)
+++ python/trunk/Doc/faq/design.rst Tue Nov 24 15:27:02 2009
@@ -75,9 +75,9 @@
function prints fewer digits and this often results in the more sensible number
that was probably intended::
- >>> 0.2
- 0.20000000000000001
- >>> print 0.2
+ >>> 1.1 - 0.9
+ 0.20000000000000007
+ >>> print 1.1 - 0.9
0.2
One of the consequences of this is that it is error-prone to compare the result
Modified: python/trunk/Doc/library/decimal.rst
==============================================================================
--- python/trunk/Doc/library/decimal.rst (original)
+++ python/trunk/Doc/library/decimal.rst Tue Nov 24 15:27:02 2009
@@ -35,9 +35,9 @@
people learn at school." -- excerpt from the decimal arithmetic specification.
* Decimal numbers can be represented exactly. In contrast, numbers like
- :const:`1.1` do not have an exact representation in binary floating point. End
- users typically would not expect :const:`1.1` to display as
- :const:`1.1000000000000001` as it does with binary floating point.
+ :const:`1.1` and :const:`2.2` do not have an exact representations in binary
+ floating point. End users typically would not expect ``1.1 + 2.2`` to display
+ as :const:`3.3000000000000003` as it does with binary floating point.
* The exactness carries over into arithmetic. In decimal floating point, ``0.1
+ 0.1 + 0.1 - 0.3`` is exactly equal to zero. In binary floating point, the result
@@ -193,7 +193,7 @@
>>> str(a)
'1.34'
>>> float(a)
- 1.3400000000000001
+ 1.34
>>> round(a, 1) # round() first converts to binary floating point
1.3
>>> int(a)
Modified: python/trunk/Doc/library/math.rst
==============================================================================
--- python/trunk/Doc/library/math.rst (original)
+++ python/trunk/Doc/library/math.rst Tue Nov 24 15:27:02 2009
@@ -90,7 +90,7 @@
loss of precision by tracking multiple intermediate partial sums::
>>> sum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
- 0.99999999999999989
+ 0.9999999999999999
>>> fsum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
1.0
Modified: python/trunk/Doc/library/sqlite3.rst
==============================================================================
--- python/trunk/Doc/library/sqlite3.rst (original)
+++ python/trunk/Doc/library/sqlite3.rst Tue Nov 24 15:27:02 2009
@@ -83,7 +83,7 @@
>>> for row in c:
... print row
...
- (u'2006-01-05', u'BUY', u'RHAT', 100, 35.140000000000001)
+ (u'2006-01-05', u'BUY', u'RHAT', 100, 35.14)
(u'2006-03-28', u'BUY', u'IBM', 1000, 45.0)
(u'2006-04-06', u'SELL', u'IBM', 500, 53.0)
(u'2006-04-05', u'BUY', u'MSOFT', 1000, 72.0)
@@ -601,7 +601,7 @@
>>> type(r)
<type 'sqlite3.Row'>
>>> r
- (u'2006-01-05', u'BUY', u'RHAT', 100.0, 35.140000000000001)
+ (u'2006-01-05', u'BUY', u'RHAT', 100.0, 35.14)
>>> len(r)
5
>>> r[2]
Modified: python/trunk/Doc/library/turtle.rst
==============================================================================
--- python/trunk/Doc/library/turtle.rst (original)
+++ python/trunk/Doc/library/turtle.rst Tue Nov 24 15:27:02 2009
@@ -875,7 +875,7 @@
>>> tup = (0.2, 0.8, 0.55)
>>> turtle.pencolor(tup)
>>> turtle.pencolor()
- (0.20000000000000001, 0.80000000000000004, 0.5490196078431373)
+ (0.2, 0.8, 0.5490196078431373)
>>> colormode(255)
>>> turtle.pencolor()
(51, 204, 140)
Modified: python/trunk/Doc/tutorial/floatingpoint.rst
==============================================================================
--- python/trunk/Doc/tutorial/floatingpoint.rst (original)
+++ python/trunk/Doc/tutorial/floatingpoint.rst Tue Nov 24 15:27:02 2009
@@ -115,7 +115,7 @@
... sum += 0.1
...
>>> sum
- 0.99999999999999989
+ 0.9999999999999999
Binary floating-point arithmetic holds many surprises like this. The problem
with "0.1" is explained in precise detail below, in the "Representation Error"
Modified: python/trunk/Doc/tutorial/inputoutput.rst
==============================================================================
--- python/trunk/Doc/tutorial/inputoutput.rst (original)
+++ python/trunk/Doc/tutorial/inputoutput.rst Tue Nov 24 15:27:02 2009
@@ -49,10 +49,10 @@
'Hello, world.'
>>> repr(s)
"'Hello, world.'"
- >>> str(0.1)
- '0.1'
- >>> repr(0.1)
- '0.10000000000000001'
+ >>> str(1.0/7.0)
+ '0.142857142857'
+ >>> repr(1.0/7.0)
+ '0.14285714285714285'
>>> x = 10 * 3.25
>>> y = 200 * 200
>>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y) + '...'
Modified: python/trunk/Doc/tutorial/stdlib2.rst
==============================================================================
--- python/trunk/Doc/tutorial/stdlib2.rst (original)
+++ python/trunk/Doc/tutorial/stdlib2.rst Tue Nov 24 15:27:02 2009
@@ -362,10 +362,13 @@
becomes significant if the results are rounded to the nearest cent::
>>> from decimal import *
- >>> Decimal('0.70') * Decimal('1.05')
+ >>> x = Decimal('0.70') * Decimal('1.05')
+ >>> x
Decimal('0.7350')
- >>> .70 * 1.05
- 0.73499999999999999
+ >>> x.quantize(Decimal('0.01')) # round to nearest cent
+ Decimal('0.74')
+ >>> round(.70 * 1.05, 2) # same calculation with floats
+ 0.73
The :class:`Decimal` result keeps a trailing zero, automatically inferring four
place significance from multiplicands with two place significance. Decimal
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