You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
142 lines
4.6 KiB
142 lines
4.6 KiB
"""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
|
|
|