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/Lib/fpformat.py

http://unladen-swallow.googlecode.com/
Python | 145 lines | 121 code | 5 blank | 19 comment | 0 complexity | 2bf9e08a75526a1214af672ccafac25a MD5 | raw file
  1"""General floating point formatting functions.
  2
  3Functions:
  4fix(x, digits_behind)
  5sci(x, digits_behind)
  6
  7Each takes a number or a string and a number of digits as arguments.
  8
  9Parameters:
 10x:             number to be formatted; or a string resembling a number
 11digits_behind: number of digits behind the decimal point
 12"""
 13from warnings import warnpy3k
 14warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2)
 15del warnpy3k
 16
 17import re
 18
 19__all__ = ["fix","sci","NotANumber"]
 20
 21# Compiled regular expression to "decode" a number
 22decoder = 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
 29try:
 30    class NotANumber(ValueError):
 31        pass
 32except TypeError:
 33    NotANumber = 'fpformat.NotANumber'
 34
 35def 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
 50def 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
 64def 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
 90def 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
106def 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
138def 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