Develop Reference

Is there a way to check if every character in a string conforms to the set RE conditions?

I've been re-learning python over the last 2 days, and decided to use regular expression [here out referred to as RE] for the first time (in conjunction with tkinter), its exceptionally confusing.
I'm trying to check every character in a string is a number or period, however this has proven difficult for me to wrap my head around.
Here is the code:
def matchFloat(string, search=re.compile(r'[0-9.]').search):
return bool(search(string))
def matchInt(string, search=re.compile(r'[0-9]').search):
return bool(search(string))
def callbackFloat(P):
if matchFloat(P) or P == "":
return True
else:
return False
def callbackInt(P):
if matchInt(P) or P == "":
return True
else:
return False
The first character entered into my enter box [see below] is forced to be a number or . (in the Floats case), however RE search() only requires 1 of the characters to meet the conditions for it to return True.
So in short, Is there a way to only return True if every character in a string conforms to the set RE conditions?
Any help is appreciated, thank you in advanced!
Images:
As you can see, I'm quite new to this.
Disallowed Characters In Box

This thread may be helpful as it covers the topic of tkinter input validation.
However, quick answer to your question:
search(r"^[0-9]+$", string)
would match an integer string. The RE pattern means "one or more digits, extending from the beginning of the string to the end". This can also be shortened to r"^\d+$".
You could also use the re.fullmatch() method:
fullmatch(r"[0-9]+", string)
And for the sake of completeness, I'll point out that you don't need to do this work yourself. You can determine if a string represents an integer with string.isdigit(), string.isdecimal(), or string.isnumeric() methods.
As for checking whether a string is a float, the Pythonic way is to just try converting to a float and catch the exception if it fails:
try:
num = float(string)
except:
print("not a float")

Why does the str.isdigit always output the opposite result

def is_valid_zip(zip_code):
"""Returns whether the input string is a valid (5 digit) zip code
"""
if (len(zip_code) == 5) and (str.isnumeric == True):
return True
else :
return False

First of all, it should be str.isnumeric() == True as that's calling the isnumeric function. Second of all you should be really using str.isdigit().
str.isnumeric()
In Python, decimal characters (like: 0, 1, 2..), digits (like: subscript, superscript), and characters having Unicode numeric value property (like: fraction, roman numerals, currency numerators) are all considered numeric characters. Therefore even japanese character for 1, 2 and 3 would pass this check.
str.isdigit()
On the other hand isdigit() will only return True if all characters in a string are digits. If not, it returns False.
source: https://www.programiz.com/python-programming/methods/string/isdigit

A few point to discuss. Regarding your condition:
str.isnumeric == True
That thing on the left side is the function itself, not a call to the function giving a result, the latter would be some_string.isnumeric().
The chances of the function object being equal to true are somewhere between zero and a very, very small number :-)
It's also redundant to compare boolean values against boolean constants since the result of the comparison is just another boolean value. Where do you stop in that case? For example:
(((some_bool_value == True) == True) == True) != False ...
Another point, the code form if cond then return true else return false can be replaced with the much less verbose return cond.
And also keep in mind that isnumeric() allows other things than raw digits, like ¾. If you just want the digits, you're probably better off with another method. You may be tempted to instead use isdigit(), but even that allows other things than just what most would consider "normal" digits, such as allowing "90²10" as a postal code, presumably the much trendier part of Beverly Hills :-).
If you only wanted the raw digits 0-9 (which is probably the case with US postal codes like you seem to be targeting), neither isnumeric() nor isdigit() is really suitable.
An implementation of the function, taking all that into account, could be as follows:
def is_valid_zip(zip_code):
if len(zip_code) != 5:
return False
return all([x in "1234567890" for x in zip_code])

it should be zip_code.isnumeric() not str.isnumeric
Also, why don't you use regex:
import re
RE_ZIP_CODE = re.compile(r'^[0-9]{5}$') # or r'^\d{5}$' for all digit characters
def is_valid_zip(zip_code):
return RE_ZIP_CODE.search(zip_code) is not None

This should work
def is_valid_zip(zip_code):
"""Returns whether the input string is a valid (5 digit) zip code
"""
if len(zip_code) == 5 and zip_code.isnumeric():
return True
else:
return False
print(is_valid_zip("98909"))

python float is not digit? [duplicate]

This question already has answers here:
How to check if a user input is a float
(6 answers)
Closed 4 years ago.
This code returns False, but when I delete point from float it becomes True and I'm trying to understand why. Explain please
def isDigit(string):
string = string.strip()
if string[:1] == "-":
cuted = string[1:]
if cuted.isdigit():
return True
else:
return False
elif string.isdigit():
return True
else:
return False
print isDigit("-234.4")
also I know my code is not the best and I wonder how can I make it better

isdigit only checks if all the characters are digits (e.g. 0, 1, ... 9).
Therefore the string 234.4 will return False because it also contains a decimal point ., that is not a digit.
help("".isdigit)
will tell you that to be True all characters must be digits and there must be at least one character.
You could use a regular expression to do this kind of checking, for example with something like:
import re
def isnumber(x):
return re.match("-?[0-9]+([.][0-9]+)?$", x) is not None
that will accept an optional minus sign, followed by a sequence of one or more digits optionally followed by a decimal dot and more digits.
Note that floating point numbers can be accepted by a much wider syntax, including scale exponent and missing parts before and after the decimal point so don't be this strict if you're validating output from a computer. Depending on the context it may be however meaningful to refuse things like 1e4 as numbers from a human.

Let's step through your code.
if string[:1] == "-":
string[:1] means "make a string with characters from the start of string up to (but not including) index 1." If your string is "foobar", string[:1] will be "f". In your example, string[:1] will be "-"
cuted = string[1:]
This will do the opposite, producing a string that contains everything but the first character. In this case, cuted would be "234.4"
if cuted.isdigit():
return True
else:
return False
This will test if cuted is made up only of numbers. In our case, this is false, because it contains a decimal point. False is returned.
elif string.isdigit():
return True
else:
return False
If the first character was not "-", this is run instead. If you supplied "234.4", this case would be reached, and the test would fail (because "234.4" contains a decimal point), so False would be returned.
Your code appears to be valid if what you wanted was:
123.3 -> False
-123.3 -> False
123 -> True
-123 -> True
On the other hand, if you want your function to say all four of those are numbers, then you need to modify your code. The one way (probably not the best!) to do that would be to have a test case that does something like this:
If I split this string on ".", do I get two strings?
If so, are both pieces of the string digits?
If so, the string is a number.
It's not clear exactly what behavior you want.

Differentiating Python variables as str or int

I have a file that has 3 values on each line. It is a fairly random file, and any of these values can be str or int.
George, 34s, Nikon
42, absent, Alan
apple, 111, 41
marked, 15, never
...
So, I read in the line, and using split I get the first value:
theFile = r"C:\... "
tDC = open(theFile, "r")
for theLine in tDC:
a, b, c = theLine.split(',')
So far so good.
Where I'm stuck is when I try to deal with variable a. I need to deal with it differently if it is a str or if it is an int. I tried setting a = int(a), but if it is a string (e.g., 'George') then I get an error. I tried if type(a) = int or if isinstance(a,int), but neither work because all the values come in as a string!
So, how do I evaluate the value NOT looking at its assigned 'type'? Specifically, I want to read all the a's and find the maximum value of all the numbers (they'll be integers, but could be large -- six digits, perhaps).
Is there a way to read in the line so that numbers come in as numbers and strings come in as strings, or perhaps there is a way to evaluate the value itself without looking at the type?

The first point is that you need some rule that tells you which values are integers and which ones aren't. In a data set that includes things like 32s, I'm not sure it makes sense to just treat anything that could be an integer as if it were.
But, for simplicity, let's assume that is the rule you want: anything that could be an integer is. So, int(a) is already pretty close; the only issue is that it can fail. What do you do with that?
Python is designed around EAFP: it's Easier to Ask Forgiveness than Permission. Try something, and then deal with the fact that it might fail. As Cyber suggests, with a try statement:
try:
intvalue = int(a)
except ValueError:
# Oops, it wasn't an int, and that's fine
pass
else:
# It was an int, and now we have the int value
maxvalue = max(maxvalue, intvalue)

isalpha() Returns "True" if all characters in the string are in the alphabet
isnumeric() Returns "True" if all characters in the string are numeric
so;
data="Hello World"
print(data.isnumeric()) #it will retuns with False
print(data.isalpha()) # True
Sorry for my soulles answer, I just came here for same issue, I found a different way and wanted to share with you

values = theLine.split(',')
for value in values:
try:
number = int(value)
# process as number
except ValueError:
# process value as string

this :
def ret_var(my_var: int) -> int:
try:
intvalue = int(my_var)
return my_var
except ValueError:
print("my_var not int!")

Python: How to refer to a digit in a string by its index?

I feel like this is a simple question, but it keeps escaping me...
If I had a string, say, "1010101", how would I refer to the first digit in the string by its index?

You can get the first element of any sequence with [0]. Since a string is a sequence of characters, you're looking for s[0]:
>>> s = "1010101"
>>> s[0]
'1'
For a detailed explanation, refer to the Python tutorial on strings.

Negative indexes count from the right side.
digit = mystring[-1]

In Python, a sting is something called, subscriptable. That means that you can access the different parts using square brackets, just like you can with a list.
If you want to get the first character of the string, then you can simply use my_string[0].
If you need to get the last (character) in a string (the final 1 in the string you provided), then use my_string[-1].
If you originally have an int (or a long) and you are looking for the last digit, you are best off using % (modulous) (10101 % 10 => 1).
If you have a float, on the other hand, you are best of str(my_float)[-1]