This article will discuss two different ways to check if a given string contains a number or float only.
Table of contents
- Use Regex to check if string contains only a number or float
- Use Exception Handling to check if string contains only a number or float
Use Regex to check if a string contains only a number/float in Python
In Python, the regex module provides a function regex.search(), which accepts a pattern and a string as arguments. Then it looks for the pattern in the given string. If a match is found, it returns a Match object; otherwise returns None. We will use this regex.search() function to check if a string contains a float or not. For that we will use the regex pattern “[-+]?\d*.?\d+(?:[eE][-+]?\d+)?$”. This pattern validates the following points in a string,
- The string must start with a decimal or a symbol i.e. plus or minus.
- After first symbol, there can be digits and then an optional dot and then again some digits.
- The string must end with digits only.
- Also, there can be an exponent symbol i.e. either ‘e’ or ‘E’.
Let’s create a function that will use the above-mentioned regex pattern to check if the given string contains a number or float only,
import re
def is_number_or_float(sample_str):
''' Returns True if the string contains only
number or float '''
result = True
if re.search("[-+]?\d*\.?\d+(?:[eE][-+]?\d+)?$", sample_str) is None:
result = False
return result
Now we will test this function with different types of strings to validate that it identifies the string representation of numbers and floats.
For example,
print( is_number_or_float("56.453") )
print( is_number_or_float("-134.2454") )
print( is_number_or_float("454") )
print( is_number_or_float("-1454.7") )
print( is_number_or_float("0.1") )
print( is_number_or_float("abc134.2454edf") )
print( is_number_or_float("abc") )
Output:
True True True True True False False
Analysis of the returned values,
- It returned True for “56.453” because it contains only digits and a dot.
- It returned True for “-134.2454” because it contains a minus symbol and digits and a dot.
- It returned True for “454” because it contains only digits.
- It returned True for “-1454.7” because it contains a minus symbol, digits and a dot.
- It returned True for “0.1” because it contains a dot and digits
- It returned False for “abc134.2454edf” because it contains some alphabets too.
- It returned False for “abc” because it contains some alphabets too.
This proves that our function can check if the given string contains a number or float only.
Use Exceptional handling to check if a string contains only a number/float
We can pass the given string to the float() function. If string contains the correct representation of a number or float then it returns the float value, otherwise it raises a ValueError. We can catch this error and validate if string is float. We have created a function that will use the exception handling and float() function to check if given string object contains a float only,
def is_number(sample_str):
""" Returns True if string contains only a
number or float """
result = True
try:
float(sample_str)
except:
result = False
return result
Now we will test this function with different types of strings to validate that it identifies the string representation of numbers and floats.
For example,
print( is_number("56.453") )
print( is_number("-134.2454") )
print( is_number("454") )
print( is_number("-1454.7") )
print( is_number("0.1") )
print( is_number("abc134.2454edf") )
print( is_number("abc") )
Output:
True True True True True False False
Analysis of the returned values,
- It returned True for “56.453” because it contains only digits and a dot.
- It returned True for “-134.2454” because it contains a minus symbol and digits and a dot.
- It returned True for “454” because it contains only digits.
- It returned True for “-1454.7” because it contains a minus symbol, digits and a dot.
- It returned True for “0.1” because it contains a dot and digits
- It returned False for “abc134.2454edf” because it contains some alphabets too.
- It returned False for “abc” because it contains some alphabets too.
This proves that our function can check if the given string contains a number or float only.
The complete example is as follows,
print("********** Using Regex **********")
import re
def is_number_or_float(sample_str):
""" Returns True if string contains only a
number or float """
result = True
if re.search("[-+]?\d*\.?\d+(?:[eE][-+]?\d+)?$", sample_str) is None:
result = False
return result
print( is_number_or_float("56.453") )
print( is_number_or_float("-134.2454") )
print( is_number_or_float("454") )
print( is_number_or_float("-1454.7") )
print( is_number_or_float("0.1") )
print( is_number_or_float("abc134.2454edf") )
print( is_number_or_float("abc") )
print("********** Using Exception Handling **********")
def is_number(sample_str):
""" Returns True if string contains only a
number or float """
result = True
try:
float(sample_str)
except:
result = False
return result
print( is_number("56.453") )
print( is_number("-134.2454") )
print( is_number("454") )
print( is_number("-1454.7") )
print( is_number("0.1") )
print( is_number("abc134.2454edf") )
print( is_number("abc") )
Output:
********** Using Regex ********** True True True True True False False ********** Using Exception Handling ********** True True True True True False False
Summary:
We learned how to check if a string contains a number or a float only.