Lib/fpformat.py

   1 """General floating point formatting functions.
   2
   3 Functions:
   4 fix(x, digits_behind)
   5 sci(x, digits_behind)
   6
   7 Each takes a number or a string and a number of digits as arguments.
   8
   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 """
  13 from warnings import warnpy3k
  14 warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2)
  15 del warnpy3k
  16
  17 import re
  18
  19 __all__ = ["fix","sci","NotANumber"]
  20
  21 # Compiled regular expression to "decode" a number
  22 decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$')
  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)
  27 # \4 exponent part (empty or begins with 'e' or 'E')
  28
  29 try:
  30     class NotANumber(ValueError):
  31         pass
  32 except TypeError:
  33     NotANumber = 'fpformat.NotANumber'
  34
  35 def extract(s):
  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
  49
  50 def unexpo(intpart, fraction, expo):
  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
  63
  64 def roundfrac(intpart, fraction, digs):
  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, ''
  89
  90 def fix(x, digs):
  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."""
  94     if type(x) != type(''): x = repr(x)
  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
 105
 106 def sci(x, digs):
 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."""
 110     if type(x) != type(''): x = repr(x)
 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
 132     e = repr(abs(expo))
 133     e = '0'*(3-len(e)) + e
 134     if expo < 0: e = '-' + e
 135     else: e = '+' + e
 136     return s + 'e' + e
 137
 138 def test():
 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