Python determines whether a string is a letter or a number (floating point)

STR is string s as String

Str.isalnum () All characters are numbers or letters

Str.isalpha () All characters are letters

Str.isdigit () All characters are numbers

Str.isspace () All characters are whitespace characters, \ t, \ n, \ r

Check that the string is a numeric/floating-point method

Float section

>> float (' nan ') nan>> float (' nan ') nan>> float (' nan ') nan>> float (' inf ') inf>> float (' inf ') inf>> float ('-inf ') inf>> float ('-inf ') inf

　　

The first type: the simplest

def is_number (str):    try:        # Because one exception to using float is ' nan '        if str== ' nan ':            return False        float (str)        return True    except ValueError:        return False        # Float Exception Example >>> float (' nan ') nan

　　

Using complex ()

def is_number (s):    try:        complex (s) # for int, long, float and complex    except ValueError:        return false< C13/>return True

　　

Synthesis 1

def is_number (s):    try:        float (s) # for int, long and float    except ValueError:        try:            complex (s) # For complex        except ValueError:            return False    return True

　　

Synthesis 2-still not fully recognized

def is_number (n):    is_number = True    try:        num = float (n)        # check "nan"         is_number = num = = num   # or use ' m Ath.isnan (num) '    except valueerror:        is_number = False    return is_number    >>> is_number (' Nan ')   false>>> is_number (' nan ')  False>>> is_number (' 123 ')  true>>> is_number (' -123 ') true>>> is_number (' -1.12 ') True >>> is_number (' abc ')  false>>> is_number (' inf ')  True

　　

The second type: can only be judged as integers

Using IsNumeric ()

# str must be Uniconde mode >>> str = u "345" >>> str.isnumeric () True

　　

Http://www.tutorialspoint.com/python/string_isnumeric.htm

Http://docs.python.org/2/howto/unicode.html

Using IsDigit ()

Https://docs.python.org/2/library/stdtypes.html#str.isdigit

>>> str = "one" >>> print str.isdigit () true>>> str = "3.14" >>> print str.isdigit () false>>> str = "AAA" >>> print str.isdigit () False

　　

Use INT ()

def is_int (str):    try:        int (str)        return True    except ValueError:        return False

　　

Third: Using the regular (safest method)

Import redef is_number (num):    pattern = re.compile (R ' ^[-+]?[ -0-9]\d*\.\d*| [-+]?\.? [0-9]\d*$ ')    result = Pattern.match (num)    if result:        return True    else:        return False                >> : Is_number (' 1 ') True>>>: Is_number (' 111 ') True>>>: Is_number (' 11.1 ') true>>>: Is_ Number (' -11.1 ') True>>>: Is_number (' inf ') False>>>: Is_number ('-inf ') False

Original: Python determines whether a string is a letter or a number (floating point)

Python determines whether a string is a letter or a number (floating point)