| """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 |
| """ |
| |
| import re |
| |
| __all__ = ["fix","sci","NotANumber"] |
| |
| # Compiled regular expression to "decode" a number |
| decoder = re.compile(r'^([-+]?)0*(\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) |
| 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 = `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 = `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 = `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 |