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[OpenSPARC-T2-SAM] / sam-t2 / devtools / v8plus / html / python / lib / decimal-recipes.html
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55<H2><A NAME="SECTION007670000000000000000"></A><A NAME="decimal-recipes"></A>
56<BR>
575.6.7 Recipes
58</H2>
59
60<P>
61Here are a few recipes that serve as utility functions and that demonstrate
62ways to work with the <tt class="class">Decimal</tt> class:
63
64<P>
65<div class="verbatim"><pre>
66def moneyfmt(value, places=2, curr='', sep=',', dp='.',
67 pos='', neg='-', trailneg=''):
68 """Convert Decimal to a money formatted string.
69
70 places: required number of places after the decimal point
71 curr: optional currency symbol before the sign (may be blank)
72 sep: optional grouping separator (comma, period, space, or blank)
73 dp: decimal point indicator (comma or period)
74 only specify as blank when places is zero
75 pos: optional sign for positive numbers: '+', space or blank
76 neg: optional sign for negative numbers: '-', '(', space or blank
77 trailneg:optional trailing minus indicator: '-', ')', space or blank
78
79 &gt;&gt;&gt; d = Decimal('-1234567.8901')
80 &gt;&gt;&gt; moneyfmt(d, curr='$')
81 '-$1,234,567.89'
82 &gt;&gt;&gt; moneyfmt(d, places=0, sep='.', dp='', neg='', trailneg='-')
83 '1.234.568-'
84 &gt;&gt;&gt; moneyfmt(d, curr='$', neg='(', trailneg=')')
85 '($1,234,567.89)'
86 &gt;&gt;&gt; moneyfmt(Decimal(123456789), sep=' ')
87 '123 456 789.00'
88 &gt;&gt;&gt; moneyfmt(Decimal('-0.02'), neg='&lt;', trailneg='&gt;')
89 '&lt;.02&gt;'
90
91 """
92 q = Decimal((0, (1,), -places)) # 2 places --&gt; '0.01'
93 sign, digits, exp = value.quantize(q).as_tuple()
94 assert exp == -places
95 result = []
96 digits = map(str, digits)
97 build, next = result.append, digits.pop
98 if sign:
99 build(trailneg)
100 for i in range(places):
101 if digits:
102 build(next())
103 else:
104 build('0')
105 build(dp)
106 i = 0
107 while digits:
108 build(next())
109 i += 1
110 if i == 3 and digits:
111 i = 0
112 build(sep)
113 build(curr)
114 if sign:
115 build(neg)
116 else:
117 build(pos)
118 result.reverse()
119 return ''.join(result)
120
121def pi():
122 """Compute Pi to the current precision.
123
124 &gt;&gt;&gt; print pi()
125 3.141592653589793238462643383
126
127 """
128 getcontext().prec += 2 # extra digits for intermediate steps
129 three = Decimal(3) # substitute "three=3.0" for regular floats
130 lasts, t, s, n, na, d, da = 0, three, 3, 1, 0, 0, 24
131 while s != lasts:
132 lasts = s
133 n, na = n+na, na+8
134 d, da = d+da, da+32
135 t = (t * n) / d
136 s += t
137 getcontext().prec -= 2
138 return +s # unary plus applies the new precision
139
140def exp(x):
141 """Return e raised to the power of x. Result type matches input type.
142
143 &gt;&gt;&gt; print exp(Decimal(1))
144 2.718281828459045235360287471
145 &gt;&gt;&gt; print exp(Decimal(2))
146 7.389056098930650227230427461
147 &gt;&gt;&gt; print exp(2.0)
148 7.38905609893
149 &gt;&gt;&gt; print exp(2+0j)
150 (7.38905609893+0j)
151
152 """
153 getcontext().prec += 2
154 i, lasts, s, fact, num = 0, 0, 1, 1, 1
155 while s != lasts:
156 lasts = s
157 i += 1
158 fact *= i
159 num *= x
160 s += num / fact
161 getcontext().prec -= 2
162 return +s
163
164def cos(x):
165 """Return the cosine of x as measured in radians.
166
167 &gt;&gt;&gt; print cos(Decimal('0.5'))
168 0.8775825618903727161162815826
169 &gt;&gt;&gt; print cos(0.5)
170 0.87758256189
171 &gt;&gt;&gt; print cos(0.5+0j)
172 (0.87758256189+0j)
173
174 """
175 getcontext().prec += 2
176 i, lasts, s, fact, num, sign = 0, 0, 1, 1, 1, 1
177 while s != lasts:
178 lasts = s
179 i += 2
180 fact *= i * (i-1)
181 num *= x * x
182 sign *= -1
183 s += num / fact * sign
184 getcontext().prec -= 2
185 return +s
186
187def sin(x):
188 """Return the sine of x as measured in radians.
189
190 &gt;&gt;&gt; print sin(Decimal('0.5'))
191 0.4794255386042030002732879352
192 &gt;&gt;&gt; print sin(0.5)
193 0.479425538604
194 &gt;&gt;&gt; print sin(0.5+0j)
195 (0.479425538604+0j)
196
197 """
198 getcontext().prec += 2
199 i, lasts, s, fact, num, sign = 1, 0, x, 1, x, 1
200 while s != lasts:
201 lasts = s
202 i += 2
203 fact *= i * (i-1)
204 num *= x * x
205 sign *= -1
206 s += num / fact * sign
207 getcontext().prec -= 2
208 return +s
209</pre></div>
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