It is bad because it looks like the value should be 37. If you see an integer that starts with a 0, in Python 2, this is (deprecated) octal syntax. Making ambiguous Python 2 octals compatible with Python 3 > 0xffffff # the color, white, max values for red, green, and blue > 0o755 # read, write, execute perms for owner, read & ex for group & others This can be useful when describing binary flags, file permissions in code, or hex values for colors - for example, note no quotes: > 0b10101 # binary flags You can use the apropos prefixes to get automatic conversion to integers with the following literals. If your motivation is to have your own code clearly represent hard-coded specific values, however, you may not need to convert from the bases - you can let Python do it for you automatically with the correct syntax. If you don't know the base in advance, but you do know they will have the correct prefix, Python can infer this for you if you pass 0 as the base: > int("0b11111", 0) Note you can prefix them with what Python expects for its literals (see below) or remove the prefix: > int("0b11111", 2) Other conversions, ints to and from strings and literals:Ĭonversions from various bases, and you should know the base in advance (10 is the default). If you're mixing them, you may be setting yourself up for problems later. It's good that you ask to do these separately. I just want to know how to parse a float string to a float, and (separately) an int string to an int. In Python, how can I parse a numeric string like "545.2222" to its corresponding float value, 542.2222? Or parse the string "31" to an integer, 31? The method locale.atoi is also available, but the argument should be an integer. In this example with French locale, the comma is correctly handled as a decimal mark: > import locale In the majority of countries of the world, commas are used for decimal marks instead of periods. In this example with American locale, the comma is handled properly as a separator: > import locale In the United States and the UK, commas can be used as a thousands separator. The locale.atof method converts to a float in one step once the locale has been set for the desired number convention.Įxample 1 - United States number conventions Instead, use methods in locale to convert the strings to numbers and interpret commas correctly. You should consider the possibility of commas in the string representation of a number, for cases like float("545,545.2222") which throws an exception. But if you're writing life-critical software in a duck-typing prototype language like Python, then you've got much larger problems. The float(.) line of code can failed for any of a thousand reasons that have nothing to do with the contents of the string. Don't use this code on life-critical software!Ĭatching broad exceptions this way, killing canaries and gobbling the exception creates a tiny chance that a valid float as string will return false. You think you know what numbers are? You are not so good as you think! Not big surprise. "+1e1^5" False Fancy exponent not interpreted "0E0" True Exponential, move dot 0 places "infinityandBEYOND" False Extra characters wreck it "12 34" False Spaces not allowed on interior 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 Check it that Python3 has different behavior for what strings are convertable to float. The below unit tests were done using python2. Python2 method to check if a string is a float: def is_float(value):įor the Python3 version of is_float see: Checking if a string can be converted to float in PythonĪ 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:
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