New submission from John Joseph Morelli <johnjmore...@hotmail.com>:
I first noticed this and reported it on the W3 Schools Tutorial, the section
entitled "Add Two Numbers with User Input"
There were many behaviors that I did not understand, but for this bug report, I
will state that the input statements present seem to return a string and under
most situations will return an error if the user inputs a real number like 2.8.
However, under a very specific situation, it will truncate 2.8 to 2 without
error.
After further investigation, I believe the following session in the IDLE's
output window and editor illustrates this inconsistent behavior. Note that I
have added comments after copying the session here...
>>> print(x) #want to ensure new session has x as undefined
Traceback (most recent call last):
File "<pyshell#23>", line 1, in <module>
print(x)
NameError: name 'x' is not defined # confirmed x is undefined
>>> x="2" # define x as the string "2"
>>> print(x)
2
>>> print(type(x)) # confirm that x is a string value of "2"
<class 'str'>
>>> y=int(x) # convert string value of "2" to integer of 2 -
# according to documentation this should work - see "If x is not a
# number or if base is given, then x must be a string, bytes, or
# bytearray instance representing an integer literal in radix base."
# at link --> https://docs.python.org/3.9/library/functions.html#int
>>> print(type(y)) # ensure y is type int
<class 'int'>
>>> print(y)
2
>>> z=x+".8" # create z to be the concatenation of two strings "2" and ".8" =
>>> "2.8", a string representation of the real number 2.8
>>> print(z)
2.8
>>> print(type(z)) # ensure z is a string
<class 'str'>
>>> aa=int(z) # convert z to an integer (as descried in the link
# above, this should NOT work
Traceback (most recent call last):
File "<pyshell#34>", line 1, in <module>
aa=int(z)
ValueError: invalid literal for int() with base 10: '2.8'
>>> w="2.8" # Define w directly as the string value of 2.8 = "2.8"
>>> bb=int(w) # This should also produce an error
Traceback (most recent call last):
File "<pyshell#36>", line 1, in <module>
bb=int(w)
ValueError: invalid literal for int() with base 10: '2.8'
>>> a='2.8'
>>> b=int(a)
Traceback (most recent call last):
File "<pyshell#38>", line 1, in <module>
b=int(a)
ValueError: invalid literal for int() with base 10: '2.8'
>>> print(type(a)) # Ensure a is a string
<class 'str'>
>>> w="2"
>>> bb=int(w)
>>> print(bb)
2
>>> print(type(bb))
<class 'int'>
>>> test=int(input("What is test value? ")) #lets try inputting a
# real number but as an argument to int and assigning it to test
What is test value? 2.8 # this should not work either
Traceback (most recent call last):
File "<pyshell#46>", line 1, in <module>
test=int(input("What is test value? "))
ValueError: invalid literal for int() with base 10: '2.8'
>>> # So everything here is working as expected, but...
Here is code from the IDLE editor... a file called testinput1.py
x = int(1)
y = input("Type a number: ")
print(type(y))
int_y = int(2.8) #conver y to an integer 2 and assign to int_y
z = int("3")
print(x)
print(y)
print(int_y)
print(z)
# I can find no documentation to suggest this should work, but it does. Here
is the output in IDLE's shell
Type a number: 2.8
<class 'str'>
1
2.8
2
3
Now, if I immediately go into the shell while the variables remain untouched
and defined...
>>> a=int(y) # Correctly, this produces the expected error
Traceback (most recent call last):
File "<pyshell#47>", line 1, in <module>
a=int(y)
ValueError: invalid literal for int() with base 10: '2.8'
After extensive testing, I conclude that after input, you may immediately apply
the int() function to the resulting string, but you quickly lose that ability,
resulting in the expected error. I can find no documentation to explain this
behavior.
If I am not overlooking something, I think this should either be in the
documentation of the function int(), if it is intended to behaviour this way,
or as a bug, should be corrected.
NOTE, I just started learning Pytyon this weekend, so I may be just ignorant of
the behavior, but I have searched a good bit and found nothing suggesting this
is how int() should behalf. I have also not studied the other constructor
functions.
----------
assignee: docs@python
components: Build, Documentation, IDLE, Library (Lib), Windows
files: function_int_08Aug21.txt
messages: 399224
nosy: TheDoctor165, docs@python, paul.moore, steve.dower, terry.reedy,
tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Inconsistent Behavior of int()
type: behavior
versions: Python 3.9
Added file: https://bugs.python.org/file50205/function_int_08Aug21.txt
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue44866>
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