sys.float_info
A struct sequence holding information about the float type. It contains low level information about the precision and internal representation. The values correspond to the various floating-point constants defined in the standard header file float.h for the ‘C’ programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard [C99], ‘Characteristics of floating types’, for details.
| attribute | float.h macro | explanation |
|---|---|---|
epsilon | DBL_EPSILON | difference between 1 and the least value greater than 1 that is representable as a float |
dig | DBL_DIG | maximum number of decimal digits that can be faithfully represented in a float; see below |
mant_dig | DBL_MANT_DIG | float precision: the number of base-radix digits in the significand of a float |
max | DBL_MAX | maximum representable finite float |
max_exp | DBL_MAX_EXP | maximum integer e such that radix**(e-1) is a representable finite float |
max_10_exp | DBL_MAX_10_EXP | maximum integer e such that 10**e is in the range of representable finite floats |
min | DBL_MIN | minimum positive normalized float |
min_exp | DBL_MIN_EXP | minimum integer e such that radix**(e-1) is a normalized float |
min_10_exp | DBL_MIN_10_EXP | minimum integer e such that 10**e is a normalized float |
radix | FLT_RADIX | radix of exponent representation |
rounds | FLT_ROUNDS | integer constant representing the rounding mode used for arithmetic operations. This reflects the value of the system FLT_ROUNDS macro at interpreter startup time. See section 5.2.4.2.2 of the C99 standard for an explanation of the possible values and their meanings. |
The attribute sys.float_info.dig needs further explanation. If s is any string representing a decimal number with at most sys.float_info.dig significant digits, then converting s to a float and back again will recover a string representing the same decimal value:
>>> import sys >>> sys.float_info.dig 15 >>> s = '3.14159265358979' # decimal string with 15 significant digits >>> format(float(s), '.15g') # convert to float and back -> same value '3.14159265358979'
But for strings with more than sys.float_info.dig significant digits, this isn’t always true:
>>> s = '9876543211234567' # 16 significant digits is too many! >>> format(float(s), '.16g') # conversion changes value '9876543211234568'
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