How do I parse a string to a float or int?

stackoverflow.com › questions › 379906 › how-do-i-parse-a-string-to-a-float-or-int

>>> a = "545.2222"
>>> float(a)
545.22220000000004
>>> int(float(a))
545

Answer from Harley Holcombe on Stack Overflow

Stack Overflow

stackoverflow.com › questions › 379906 › how-do-i-parse-a-string-to-a-float-or-int

python - How do I parse a string to a float or int? - Stack Overflow

Top answer

1 of 16

3120

>>> a = "545.2222"
>>> float(a)
545.22220000000004
>>> int(float(a))
545

2 of 16

606

Python2 method to check if a string is a float:

def is_float(value):
  if value is None:
      return False
  try:
      float(value)
      return True
  except:
      return False

For the Python3 version of is_float see: Checking if a string can be converted to float in Python

A longer and more accurate name for this function could be: is_convertible_to_float(value)

What is, and is not a float in Python may surprise you:

The below unit tests were done using python2. Check it that Python3 has different behavior for what strings are convertable to float. One confounding difference is that any number of interior underscores are now allowed: (float("1_3.4") == float(13.4)) is True

val                   is_float(val) Note
--------------------  ----------   --------------------------------
""                    False        Blank string
"127"                 True         Passed string
True                  True         Pure sweet Truth
"True"                False        Vile contemptible lie
False                 True         So false it becomes true
"123.456"             True         Decimal
"      -127    "      True         Spaces trimmed
"\t\n12\r\n"          True         whitespace ignored
"NaN"                 True         Not a number
"NaNanananaBATMAN"    False        I am Batman
"-iNF"                True         Negative infinity
"123.E4"              True         Exponential notation
".1"                  True         mantissa only
"1_2_3.4"             False        Underscores not allowed
"12 34"               False        Spaces not allowed on interior
"1,234"               False        Commas gtfo
u'\x30'               True         Unicode is fine.
"NULL"                False        Null is not special
0x3fade               True         Hexadecimal
"6e7777777777777"     True         Shrunk to infinity
"1.797693e+308"       True         This is max value
"infinity"            True         Same as inf
"infinityandBEYOND"   False        Extra characters wreck it
"12.34.56"            False        Only one dot allowed
u'四'                 False        Japanese '4' is not a float.
"#56"                 False        Pound sign
"56%"                 False        Percent of what?
"0E0"                 True         Exponential, move dot 0 places
0**0                  True         0___0  Exponentiation
"-5e-5"               True         Raise to a negative number
"+1e1"                True         Plus is OK with exponent
"+1e1^5"              False        Fancy exponent not interpreted
"+1e1.3"              False        No decimals in exponent
"-+1"                 False        Make up your mind
"(1)"                 False        Parenthesis is bad

You think you know what numbers are? You are not so good as you think! Not big surprise.

Don't use this code on life-critical software!

Catching broad exceptions this way, killing canaries and gobbling the exception creates a tiny chance that a valid float as string will return false. The float(...) line of code can failed for any of a thousand reasons that have nothing to do with the contents of the string. But if you're writing life-critical software in a duck-typing prototype language like Python, then you've got much larger problems.

reddit.com › r/learnpython › python string to float conversion

r/learnpython on Reddit: Python string to float conversion

July 29, 2024 -

Hi all, I have a string a = '1721244344.700249000', I want to convert it to a floating value.

Float() is returning only 2 places after decimal point. Like 1721244344.7

Is there a way I can convert the entire string to a floating point value and get all the decimal (upto 9 places after decimal point)?

I have to use python v2.7 for this.

Edit: I do not have problem in printing the all 9 decimal places but I need the floating value so that I can subtract another value so that I get the difference with accuracy upto 9 th decimal point.

Top answer

1 of 5

I don't know what you mean: >>> a = '1721244344.700249000' >>> float(a) 1721244344.700249 These are all the decimal places. Trailing zeros will always be omitted as they are irrelevant. If you want to show them, do so when you output the value: >>> print(a.format("{:.9}")) 1721244344.700249000

2 of 5

I have to use python v2.7 for this. ?????????!

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