Home | History | Annotate | Download | only in Lib 
      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'^([-+]?)(\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     intpart = intpart.lstrip('0');
     45     if sign == '+': sign = ''
     46     if fraction: fraction = fraction[1:]
     47     if exppart: expo = int(exppart[1:])
     48     else: expo = 0
     49     return sign, intpart, fraction, expo
     50 
     51 def unexpo(intpart, fraction, expo):
     52     """Remove the exponent by changing intpart and fraction."""
     53     if expo > 0: # Move the point left
     54         f = len(fraction)
     55         intpart, fraction = intpart + fraction[:expo], fraction[expo:]
     56         if expo > f:
     57             intpart = intpart + '0'*(expo-f)
     58     elif expo < 0: # Move the point right
     59         i = len(intpart)
     60         intpart, fraction = intpart[:expo], intpart[expo:] + fraction
     61         if expo < -i:
     62             fraction = '0'*(-expo-i) + fraction
     63     return intpart, fraction
     64 
     65 def roundfrac(intpart, fraction, digs):
     66     """Round or extend the fraction to size digs."""
     67     f = len(fraction)
     68     if f <= digs:
     69         return intpart, fraction + '0'*(digs-f)
     70     i = len(intpart)
     71     if i+digs < 0:
     72         return '0'*-digs, ''
     73     total = intpart + fraction
     74     nextdigit = total[i+digs]
     75     if nextdigit >= '5': # Hard case: increment last digit, may have carry!
     76         n = i + digs - 1
     77         while n >= 0:
     78             if total[n] != '9': break
     79             n = n-1
     80         else:
     81             total = '0' + total
     82             i = i+1
     83             n = 0
     84         total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1)
     85         intpart, fraction = total[:i], total[i:]
     86     if digs >= 0:
     87         return intpart, fraction[:digs]
     88     else:
     89         return intpart[:digs] + '0'*-digs, ''
     90 
     91 def fix(x, digs):
     92     """Format x as [-]ddd.ddd with 'digs' digits after the point
     93     and at least one digit before.
     94     If digs <= 0, the point is suppressed."""
     95     if type(x) != type(''): x = repr(x)
     96     try:
     97         sign, intpart, fraction, expo = extract(x)
     98     except NotANumber:
     99         return x
    100     intpart, fraction = unexpo(intpart, fraction, expo)
    101     intpart, fraction = roundfrac(intpart, fraction, digs)
    102     while intpart and intpart[0] == '0': intpart = intpart[1:]
    103     if intpart == '': intpart = '0'
    104     if digs > 0: return sign + intpart + '.' + fraction
    105     else: return sign + intpart
    106 
    107 def sci(x, digs):
    108     """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point
    109     and exactly one digit before.
    110     If digs is <= 0, one digit is kept and the point is suppressed."""
    111     if type(x) != type(''): x = repr(x)
    112     sign, intpart, fraction, expo = extract(x)
    113     if not intpart:
    114         while fraction and fraction[0] == '0':
    115             fraction = fraction[1:]
    116             expo = expo - 1
    117         if fraction:
    118             intpart, fraction = fraction[0], fraction[1:]
    119             expo = expo - 1
    120         else:
    121             intpart = '0'
    122     else:
    123         expo = expo + len(intpart) - 1
    124         intpart, fraction = intpart[0], intpart[1:] + fraction
    125     digs = max(0, digs)
    126     intpart, fraction = roundfrac(intpart, fraction, digs)
    127     if len(intpart) > 1:
    128         intpart, fraction, expo = \
    129             intpart[0], intpart[1:] + fraction[:-1], \
    130             expo + len(intpart) - 1
    131     s = sign + intpart
    132     if digs > 0: s = s + '.' + fraction
    133     e = repr(abs(expo))
    134     e = '0'*(3-len(e)) + e
    135     if expo < 0: e = '-' + e
    136     else: e = '+' + e
    137     return s + 'e' + e
    138 
    139 def test():
    140     """Interactive test run."""
    141     try:
    142         while 1:
    143             x, digs = input('Enter (x, digs): ')
    144             print x, fix(x, digs), sci(x, digs)
    145     except (EOFError, KeyboardInterrupt):
    146         pass
    147