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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

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Python String to float, float to String - AskPython

February 16, 2023 - Python provides us with the built-in float() method to convert the data type of input from String to float.

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.

Discussions

Python string to float conversion

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 More on reddit.com

r/learnpython

18

5

July 29, 2024

How I convert float to string in this case?

You shouldn't call your variable sum, as that's a name of a built in function: https://docs.python.org/3/library/functions.html#sum Your problem however, stems from trying to add a string to a float. Could you please tell me, what is Adam + 5? Well, you can't, because it makes no mathematical sense. You didn't save the string representation str(sum), so sum never changed to a string What your research found is f-strings and they are very easy to use. Try: print(f"the sum of the values is {sum}") Simply, put an f before a string starts, then any string that you want goes between " and ", while any variables or other values go between { and } More on reddit.com

r/learnpython

4

2

August 21, 2022

Python - decimal places (putting floats into a string) - Stack Overflow

where "0" refers to the first value passed into str.format, ":" says "here comes the format specification", and ".2f" means "floating point number with two decimal places of precision". This is the suggested way of formatting strings now. ... For Python version 3.6 and upwards there is also ... More on stackoverflow.com

stackoverflow.com

Quick question: Is there a way to get the first three digits of a int without converting it to a string or list?

You probably shouldn't be keeping phone numbers as ints, because they don't behave like ints. You'll never add, subtract, multiply, or divide phone numbers. You will, however, access individual digits of them, so an array is a much more appropriate type. If you absolutely must store them as ints for efficiency reasons (unlikely), then at point of use you should probably just convert them, unless that is too expensive (even more unlikely).

Remember readability is generally more important than minor performance gains, so digits(num)[:3] is much easier to understand than (num-num%le6)/le6 as skier_scott suggests doing.

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