[Python-checkins] 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

Tue Nov 24 15:27:03 CET 2009

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
