Guido van Rossum | 4acc25b | 2000-02-02 15:10:15 +0000 | [diff] [blame] | 1 | """General floating point formatting functions. |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 2 | |
Guido van Rossum | 4acc25b | 2000-02-02 15:10:15 +0000 | [diff] [blame] | 3 | Functions: |
| 4 | fix(x, digits_behind) |
| 5 | sci(x, digits_behind) |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 6 | |
Guido van Rossum | 4acc25b | 2000-02-02 15:10:15 +0000 | [diff] [blame] | 7 | Each takes a number or a string and a number of digits as arguments. |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 8 | |
Guido van Rossum | 4acc25b | 2000-02-02 15:10:15 +0000 | [diff] [blame] | 9 | Parameters: |
| 10 | x: number to be formatted; or a string resembling a number |
| 11 | digits_behind: number of digits behind the decimal point |
| 12 | """ |
Brett Cannon | fe59851 | 2008-05-10 22:11:45 +0000 | [diff] [blame] | 13 | from warnings import warnpy3k |
| 14 | warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2) |
| 15 | del warnpy3k |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 16 | |
Guido van Rossum | 9694fca | 1997-10-22 21:00:49 +0000 | [diff] [blame] | 17 | import re |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 18 | |
Skip Montanaro | eccd02a | 2001-01-20 23:34:12 +0000 | [diff] [blame] | 19 | __all__ = ["fix","sci","NotANumber"] |
| 20 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 21 | # Compiled regular expression to "decode" a number |
Guido van Rossum | 31626bc | 1997-10-24 14:46:16 +0000 | [diff] [blame] | 22 | decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$') |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 23 | # \0 the whole thing |
| 24 | # \1 leading sign or empty |
| 25 | # \2 digits left of decimal point |
| 26 | # \3 fraction (empty or begins with point) |
Guido van Rossum | 31626bc | 1997-10-24 14:46:16 +0000 | [diff] [blame] | 27 | # \4 exponent part (empty or begins with 'e' or 'E') |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 28 | |
Fred Drake | b8690fb | 1999-06-29 15:49:35 +0000 | [diff] [blame] | 29 | try: |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 30 | class NotANumber(ValueError): |
| 31 | pass |
Fred Drake | b8690fb | 1999-06-29 15:49:35 +0000 | [diff] [blame] | 32 | except TypeError: |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 33 | NotANumber = 'fpformat.NotANumber' |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 34 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 35 | def extract(s): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 36 | """Return (sign, intpart, fraction, expo) or raise an exception: |
| 37 | sign is '+' or '-' |
| 38 | intpart is 0 or more digits beginning with a nonzero |
| 39 | fraction is 0 or more digits |
| 40 | expo is an integer""" |
| 41 | res = decoder.match(s) |
| 42 | if res is None: raise NotANumber, s |
| 43 | sign, intpart, fraction, exppart = res.group(1,2,3,4) |
| 44 | if sign == '+': sign = '' |
| 45 | if fraction: fraction = fraction[1:] |
| 46 | if exppart: expo = int(exppart[1:]) |
| 47 | else: expo = 0 |
| 48 | return sign, intpart, fraction, expo |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 49 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 50 | def unexpo(intpart, fraction, expo): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 51 | """Remove the exponent by changing intpart and fraction.""" |
| 52 | if expo > 0: # Move the point left |
| 53 | f = len(fraction) |
| 54 | intpart, fraction = intpart + fraction[:expo], fraction[expo:] |
| 55 | if expo > f: |
| 56 | intpart = intpart + '0'*(expo-f) |
| 57 | elif expo < 0: # Move the point right |
| 58 | i = len(intpart) |
| 59 | intpart, fraction = intpart[:expo], intpart[expo:] + fraction |
| 60 | if expo < -i: |
| 61 | fraction = '0'*(-expo-i) + fraction |
| 62 | return intpart, fraction |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 63 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 64 | def roundfrac(intpart, fraction, digs): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 65 | """Round or extend the fraction to size digs.""" |
| 66 | f = len(fraction) |
| 67 | if f <= digs: |
| 68 | return intpart, fraction + '0'*(digs-f) |
| 69 | i = len(intpart) |
| 70 | if i+digs < 0: |
| 71 | return '0'*-digs, '' |
| 72 | total = intpart + fraction |
| 73 | nextdigit = total[i+digs] |
| 74 | if nextdigit >= '5': # Hard case: increment last digit, may have carry! |
| 75 | n = i + digs - 1 |
| 76 | while n >= 0: |
| 77 | if total[n] != '9': break |
| 78 | n = n-1 |
| 79 | else: |
| 80 | total = '0' + total |
| 81 | i = i+1 |
| 82 | n = 0 |
| 83 | total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1) |
| 84 | intpart, fraction = total[:i], total[i:] |
| 85 | if digs >= 0: |
| 86 | return intpart, fraction[:digs] |
| 87 | else: |
| 88 | return intpart[:digs] + '0'*-digs, '' |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 89 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 90 | def fix(x, digs): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 91 | """Format x as [-]ddd.ddd with 'digs' digits after the point |
| 92 | and at least one digit before. |
| 93 | If digs <= 0, the point is suppressed.""" |
Walter Dörwald | 70a6b49 | 2004-02-12 17:35:32 +0000 | [diff] [blame] | 94 | if type(x) != type(''): x = repr(x) |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 95 | try: |
| 96 | sign, intpart, fraction, expo = extract(x) |
| 97 | except NotANumber: |
| 98 | return x |
| 99 | intpart, fraction = unexpo(intpart, fraction, expo) |
| 100 | intpart, fraction = roundfrac(intpart, fraction, digs) |
| 101 | while intpart and intpart[0] == '0': intpart = intpart[1:] |
| 102 | if intpart == '': intpart = '0' |
| 103 | if digs > 0: return sign + intpart + '.' + fraction |
| 104 | else: return sign + intpart |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 105 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 106 | def sci(x, digs): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 107 | """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point |
| 108 | and exactly one digit before. |
| 109 | If digs is <= 0, one digit is kept and the point is suppressed.""" |
Walter Dörwald | 70a6b49 | 2004-02-12 17:35:32 +0000 | [diff] [blame] | 110 | if type(x) != type(''): x = repr(x) |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 111 | sign, intpart, fraction, expo = extract(x) |
| 112 | if not intpart: |
| 113 | while fraction and fraction[0] == '0': |
| 114 | fraction = fraction[1:] |
| 115 | expo = expo - 1 |
| 116 | if fraction: |
| 117 | intpart, fraction = fraction[0], fraction[1:] |
| 118 | expo = expo - 1 |
| 119 | else: |
| 120 | intpart = '0' |
| 121 | else: |
| 122 | expo = expo + len(intpart) - 1 |
| 123 | intpart, fraction = intpart[0], intpart[1:] + fraction |
| 124 | digs = max(0, digs) |
| 125 | intpart, fraction = roundfrac(intpart, fraction, digs) |
| 126 | if len(intpart) > 1: |
| 127 | intpart, fraction, expo = \ |
| 128 | intpart[0], intpart[1:] + fraction[:-1], \ |
| 129 | expo + len(intpart) - 1 |
| 130 | s = sign + intpart |
| 131 | if digs > 0: s = s + '.' + fraction |
Walter Dörwald | 70a6b49 | 2004-02-12 17:35:32 +0000 | [diff] [blame] | 132 | e = repr(abs(expo)) |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 133 | e = '0'*(3-len(e)) + e |
| 134 | if expo < 0: e = '-' + e |
| 135 | else: e = '+' + e |
| 136 | return s + 'e' + e |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 137 | |
Guido van Rossum | 29be3b9 | 1992-03-15 21:37:43 +0000 | [diff] [blame] | 138 | def test(): |
Guido van Rossum | 54f22ed | 2000-02-04 15:10:34 +0000 | [diff] [blame] | 139 | """Interactive test run.""" |
| 140 | try: |
| 141 | while 1: |
| 142 | x, digs = input('Enter (x, digs): ') |
| 143 | print x, fix(x, digs), sci(x, digs) |
| 144 | except (EOFError, KeyboardInterrupt): |
| 145 | pass |