Python to determine whether the string is a letter or a number (floating-point number) a variety of methods

str is a string s is a string

() All characters are numeric or alphabetic

() All characters are letters

() All characters are numbers

() All characters are blank characters, t, n, r

Checking that a string is a number/float method

float part

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

The first: the simplest

def is_number(str):
  try:
    # Because the one exception to using floats is 'NaN'
    if str=='NaN':
      return False
    float(str)
    return True
  except ValueError:
    return False
floatillustrative example of an exception
 >>> float('NaN')
 nan

Using complex()

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

Composite 2 - still not fully recognized

def is_number(n):
  is_number = True
  try:
    num = float(n)
    # Check "nan"
    is_number = num == num  # Or use `(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: can only be judged as an integer

Using isnumeric()

# str must be uniconde mode
>>> str = u"345"
>>> ()True
/python/string_isnumeric.htm
/2/howt...

Using isdigit()

/2/lib...
>>> str = "11"
>>> print ()
True
>>> str = "3.14"
>>> print ()
False
>>> str = "aaa"
>>> print ()
False

Using int()

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

Third: use regular (safest method)

import re
def is_number(num):
  pattern = (r'^[-+]?[-0-9]\d*\.\d*|[-+]?\.?[0-9]\d*$')
  result = (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

summarize

The above is a small introduction to Python to determine whether the string is a letter or a number (floating point) of the various methods, I hope to help you, if you have any questions please leave me a message, I will reply to you in a timely manner. Here also thank you very much for your support of my website!