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

ID : 279

viewed : 69

Tags : pythonparsingfloating-pointtype-conversionintegerpython

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

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`def is_float(value): try: float(value) return True except: return False `

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

`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 "1,234" 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.

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.

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`def num(s): try: return int(s) except ValueError: return float(s) `

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This is another method which deserves to be mentioned here, ast.literal_eval:

This can be used for safely evaluating strings containing Python expressions from untrusted sources without the need to parse the values oneself.

That is, a safe 'eval'

`>>> import ast >>> ast.literal_eval("545.2222") 545.2222 >>> ast.literal_eval("31") 31 `

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`float(x) if '.' in x else int(x) `