JezK
Edit File: fpformat.py
"""General floating point formatting functions. Functions: fix(x, digits_behind) sci(x, digits_behind) Each takes a number or a string and a number of digits as arguments. Parameters: x: number to be formatted; or a string resembling a number digits_behind: number of digits behind the decimal point """ from warnings import warnpy3k warnpy3k("the fpformat module has been removed in Python 3.0", stacklevel=2) del warnpy3k import re __all__ = ["fix","sci","NotANumber"] # Compiled regular expression to "decode" a number decoder = re.compile(r'^([-+]?)(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$') # \0 the whole thing # \1 leading sign or empty # \2 digits left of decimal point # \3 fraction (empty or begins with point) # \4 exponent part (empty or begins with 'e' or 'E') try: class NotANumber(ValueError): pass except TypeError: NotANumber = 'fpformat.NotANumber' def extract(s): """Return (sign, intpart, fraction, expo) or raise an exception: sign is '+' or '-' intpart is 0 or more digits beginning with a nonzero fraction is 0 or more digits expo is an integer""" res = decoder.match(s) if res is None: raise NotANumber, s sign, intpart, fraction, exppart = res.group(1,2,3,4) intpart = intpart.lstrip('0'); if sign == '+': sign = '' if fraction: fraction = fraction[1:] if exppart: expo = int(exppart[1:]) else: expo = 0 return sign, intpart, fraction, expo def unexpo(intpart, fraction, expo): """Remove the exponent by changing intpart and fraction.""" if expo > 0: # Move the point left f = len(fraction) intpart, fraction = intpart + fraction[:expo], fraction[expo:] if expo > f: intpart = intpart + '0'*(expo-f) elif expo < 0: # Move the point right i = len(intpart) intpart, fraction = intpart[:expo], intpart[expo:] + fraction if expo < -i: fraction = '0'*(-expo-i) + fraction return intpart, fraction def roundfrac(intpart, fraction, digs): """Round or extend the fraction to size digs.""" f = len(fraction) if f <= digs: return intpart, fraction + '0'*(digs-f) i = len(intpart) if i+digs < 0: return '0'*-digs, '' total = intpart + fraction nextdigit = total[i+digs] if nextdigit >= '5': # Hard case: increment last digit, may have carry! n = i + digs - 1 while n >= 0: if total[n] != '9': break n = n-1 else: total = '0' + total i = i+1 n = 0 total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1) intpart, fraction = total[:i], total[i:] if digs >= 0: return intpart, fraction[:digs] else: return intpart[:digs] + '0'*-digs, '' def fix(x, digs): """Format x as [-]ddd.ddd with 'digs' digits after the point and at least one digit before. If digs <= 0, the point is suppressed.""" if type(x) != type(''): x = repr(x) try: sign, intpart, fraction, expo = extract(x) except NotANumber: return x intpart, fraction = unexpo(intpart, fraction, expo) intpart, fraction = roundfrac(intpart, fraction, digs) while intpart and intpart[0] == '0': intpart = intpart[1:] if intpart == '': intpart = '0' if digs > 0: return sign + intpart + '.' + fraction else: return sign + intpart def sci(x, digs): """Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point and exactly one digit before. If digs is <= 0, one digit is kept and the point is suppressed.""" if type(x) != type(''): x = repr(x) sign, intpart, fraction, expo = extract(x) if not intpart: while fraction and fraction[0] == '0': fraction = fraction[1:] expo = expo - 1 if fraction: intpart, fraction = fraction[0], fraction[1:] expo = expo - 1 else: intpart = '0' else: expo = expo + len(intpart) - 1 intpart, fraction = intpart[0], intpart[1:] + fraction digs = max(0, digs) intpart, fraction = roundfrac(intpart, fraction, digs) if len(intpart) > 1: intpart, fraction, expo = \ intpart[0], intpart[1:] + fraction[:-1], \ expo + len(intpart) - 1 s = sign + intpart if digs > 0: s = s + '.' + fraction e = repr(abs(expo)) e = '0'*(3-len(e)) + e if expo < 0: e = '-' + e else: e = '+' + e return s + 'e' + e def test(): """Interactive test run.""" try: while 1: x, digs = input('Enter (x, digs): ') print x, fix(x, digs), sci(x, digs) except (EOFError, KeyboardInterrupt): pass