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