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55 | <H2><A NAME="SECTION007670000000000000000"></A><A NAME="decimal-recipes"></A> | |
56 | <BR> | |
57 | 5.6.7 Recipes | |
58 | </H2> | |
59 | ||
60 | <P> | |
61 | Here are a few recipes that serve as utility functions and that demonstrate | |
62 | ways to work with the <tt class="class">Decimal</tt> class: | |
63 | ||
64 | <P> | |
65 | <div class="verbatim"><pre> | |
66 | def 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 | >>> d = Decimal('-1234567.8901') | |
80 | >>> moneyfmt(d, curr='$') | |
81 | '-$1,234,567.89' | |
82 | >>> moneyfmt(d, places=0, sep='.', dp='', neg='', trailneg='-') | |
83 | '1.234.568-' | |
84 | >>> moneyfmt(d, curr='$', neg='(', trailneg=')') | |
85 | '($1,234,567.89)' | |
86 | >>> moneyfmt(Decimal(123456789), sep=' ') | |
87 | '123 456 789.00' | |
88 | >>> moneyfmt(Decimal('-0.02'), neg='<', trailneg='>') | |
89 | '<.02>' | |
90 | ||
91 | """ | |
92 | q = Decimal((0, (1,), -places)) # 2 places --> '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 | ||
121 | def pi(): | |
122 | """Compute Pi to the current precision. | |
123 | ||
124 | >>> 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 | ||
140 | def exp(x): | |
141 | """Return e raised to the power of x. Result type matches input type. | |
142 | ||
143 | >>> print exp(Decimal(1)) | |
144 | 2.718281828459045235360287471 | |
145 | >>> print exp(Decimal(2)) | |
146 | 7.389056098930650227230427461 | |
147 | >>> print exp(2.0) | |
148 | 7.38905609893 | |
149 | >>> 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 | ||
164 | def cos(x): | |
165 | """Return the cosine of x as measured in radians. | |
166 | ||
167 | >>> print cos(Decimal('0.5')) | |
168 | 0.8775825618903727161162815826 | |
169 | >>> print cos(0.5) | |
170 | 0.87758256189 | |
171 | >>> 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 | ||
187 | def sin(x): | |
188 | """Return the sine of x as measured in radians. | |
189 | ||
190 | >>> print sin(Decimal('0.5')) | |
191 | 0.4794255386042030002732879352 | |
192 | >>> print sin(0.5) | |
193 | 0.479425538604 | |
194 | >>> 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> | |
210 | ||
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247 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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