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1 """General floating point formatting functions. |
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2 |
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3 Functions: |
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4 fix(x, digits_behind) |
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5 sci(x, digits_behind) |
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6 |
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7 Each takes a number or a string and a number of digits as arguments. |
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8 |
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9 Parameters: |
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10 x: number to be formatted; or a string resembling a number |
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11 digits_behind: number of digits behind the decimal point |
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12 """ |
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13 |
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14 import re |
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15 |
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16 __all__ = ["fix","sci","NotANumber"] |
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17 |
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18 # Compiled regular expression to "decode" a number |
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19 decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$') |
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20 # \0 the whole thing |
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21 # \1 leading sign or empty |
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22 # \2 digits left of decimal point |
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23 # \3 fraction (empty or begins with point) |
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24 # \4 exponent part (empty or begins with 'e' or 'E') |
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25 |
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26 try: |
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27 class NotANumber(ValueError): |
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28 pass |
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29 except TypeError: |
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30 NotANumber = 'fpformat.NotANumber' |
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31 |
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32 def extract(s): |
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33 """Return (sign, intpart, fraction, expo) or raise an exception: |
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34 sign is '+' or '-' |
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35 intpart is 0 or more digits beginning with a nonzero |
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36 fraction is 0 or more digits |
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37 expo is an integer""" |
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38 res = decoder.match(s) |
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39 if res is None: raise NotANumber, s |
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40 sign, intpart, fraction, exppart = res.group(1,2,3,4) |
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41 if sign == '+': sign = '' |
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42 if fraction: fraction = fraction[1:] |
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43 if exppart: expo = int(exppart[1:]) |
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44 else: expo = 0 |
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45 return sign, intpart, fraction, expo |
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46 |
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47 def unexpo(intpart, fraction, expo): |
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48 """Remove the exponent by changing intpart and fraction.""" |
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49 if expo > 0: # Move the point left |
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50 f = len(fraction) |
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51 intpart, fraction = intpart + fraction[:expo], fraction[expo:] |
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52 if expo > f: |
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53 intpart = intpart + '0'*(expo-f) |
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54 elif expo < 0: # Move the point right |
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55 i = len(intpart) |
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56 intpart, fraction = intpart[:expo], intpart[expo:] + fraction |
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57 if expo < -i: |
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58 fraction = '0'*(-expo-i) + fraction |
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59 return intpart, fraction |
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60 |
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61 def roundfrac(intpart, fraction, digs): |
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62 """Round or extend the fraction to size digs.""" |
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63 f = len(fraction) |
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64 if f <= digs: |
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65 return intpart, fraction + '0'*(digs-f) |
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66 i = len(intpart) |
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67 if i+digs < 0: |
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68 return '0'*-digs, '' |
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69 total = intpart + fraction |
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70 nextdigit = total[i+digs] |
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71 if nextdigit >= '5': # Hard case: increment last digit, may have carry! |
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72 n = i + digs - 1 |
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73 while n >= 0: |
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74 if total[n] != '9': break |
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75 n = n-1 |
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76 else: |
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77 total = '0' + total |
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78 i = i+1 |
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79 n = 0 |
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80 total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1) |
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81 intpart, fraction = total[:i], total[i:] |
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82 if digs >= 0: |
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83 return intpart, fraction[:digs] |
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84 else: |
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85 return intpart[:digs] + '0'*-digs, '' |
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86 |
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87 def fix(x, digs): |
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88 """Format x as [-]ddd.ddd with 'digs' digits after the point |
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89 and at least one digit before. |
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90 If digs <= 0, the point is suppressed.""" |
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91 if type(x) != type(''): x = repr(x) |
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92 try: |
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93 sign, intpart, fraction, expo = extract(x) |
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94 except NotANumber: |
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95 return x |
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96 intpart, fraction = unexpo(intpart, fraction, expo) |
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97 intpart, fraction = roundfrac(intpart, fraction, digs) |
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98 while intpart and intpart[0] == '0': intpart = intpart[1:] |
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99 if intpart == '': intpart = '0' |
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100 if digs > 0: return sign + intpart + '.' + fraction |
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101 else: return sign + intpart |
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102 |
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103 def sci(x, digs): |
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104 """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point |
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105 and exactly one digit before. |
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106 If digs is <= 0, one digit is kept and the point is suppressed.""" |
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107 if type(x) != type(''): x = repr(x) |
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108 sign, intpart, fraction, expo = extract(x) |
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109 if not intpart: |
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110 while fraction and fraction[0] == '0': |
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111 fraction = fraction[1:] |
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112 expo = expo - 1 |
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113 if fraction: |
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114 intpart, fraction = fraction[0], fraction[1:] |
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115 expo = expo - 1 |
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116 else: |
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117 intpart = '0' |
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118 else: |
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119 expo = expo + len(intpart) - 1 |
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120 intpart, fraction = intpart[0], intpart[1:] + fraction |
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121 digs = max(0, digs) |
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122 intpart, fraction = roundfrac(intpart, fraction, digs) |
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123 if len(intpart) > 1: |
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124 intpart, fraction, expo = \ |
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125 intpart[0], intpart[1:] + fraction[:-1], \ |
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126 expo + len(intpart) - 1 |
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127 s = sign + intpart |
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128 if digs > 0: s = s + '.' + fraction |
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129 e = repr(abs(expo)) |
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130 e = '0'*(3-len(e)) + e |
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131 if expo < 0: e = '-' + e |
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132 else: e = '+' + e |
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133 return s + 'e' + e |
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134 |
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135 def test(): |
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136 """Interactive test run.""" |
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137 try: |
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138 while 1: |
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139 x, digs = input('Enter (x, digs): ') |
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140 print x, fix(x, digs), sci(x, digs) |
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141 except (EOFError, KeyboardInterrupt): |
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142 pass |