Why does Python's eval(input(“Enter input: ”)) change input's datatype?
In Python 3, I write a simple command to accept an integer input from the user thus:
x = int(input("Enter a number: "))
If I skip the int() part and simply use x = input("Enter a number: "), my input's datatype is a string, not an integer. I understand that.
However, if I use the following command:
x = eval(input("Enter a number: "))
the input's datatype is 'int'.
Why does this happen?
python eval type-conversion
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
add a comment |
In Python 3, I write a simple command to accept an integer input from the user thus:
x = int(input("Enter a number: "))
If I skip the int() part and simply use x = input("Enter a number: "), my input's datatype is a string, not an integer. I understand that.
However, if I use the following command:
x = eval(input("Enter a number: "))
the input's datatype is 'int'.
Why does this happen?
python eval type-conversion
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
1
evaltreats the input like it was written in code, doingx = 3in code makes an integer, sox = eval("3")will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed inopen(__file__,'w').close()it would delete the current executing file.
– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18
add a comment |
In Python 3, I write a simple command to accept an integer input from the user thus:
x = int(input("Enter a number: "))
If I skip the int() part and simply use x = input("Enter a number: "), my input's datatype is a string, not an integer. I understand that.
However, if I use the following command:
x = eval(input("Enter a number: "))
the input's datatype is 'int'.
Why does this happen?
python eval type-conversion
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
In Python 3, I write a simple command to accept an integer input from the user thus:
x = int(input("Enter a number: "))
If I skip the int() part and simply use x = input("Enter a number: "), my input's datatype is a string, not an integer. I understand that.
However, if I use the following command:
x = eval(input("Enter a number: "))
the input's datatype is 'int'.
Why does this happen?
python eval type-conversion
python eval type-conversion
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
edited Jun 19 '16 at 19:26
lebowski
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
asked Jun 19 '16 at 19:07
lebowskilebowski
388320
388320
maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
1
evaltreats the input like it was written in code, doingx = 3in code makes an integer, sox = eval("3")will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed inopen(__file__,'w').close()it would delete the current executing file.
– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18
add a comment |
maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
1
evaltreats the input like it was written in code, doingx = 3in code makes an integer, sox = eval("3")will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed inopen(__file__,'w').close()it would delete the current executing file.
– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18
maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
1
1
eval treats the input like it was written in code, doing x = 3 in code makes an integer, so x = eval("3") will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed in open(__file__,'w').close() it would delete the current executing file.– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18
eval treats the input like it was written in code, doing x = 3 in code makes an integer, so x = eval("3") will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed in open(__file__,'w').close() it would delete the current executing file.– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18
add a comment |
2 Answers
2
active
oldest
votes
Why does this happen?
x = eval(input("Enter a number: ")) is not the same thing as x = eval('input("Enter a number: ")')
The former first calls input(...), gets a string, e.g. '5' then evaluates it, that's why you get an int, in this manner:
>>> eval('5') # the str '5' is e.g. the value it gets after calling input(...)
5 # You get an int
While the latter (more aligned with what you were expecting), evaluates the expression 'input("Enter a number: ")'
>>> x = eval('input("Enter a number: ")')
Enter a number: 5
>>> x
'5' # Here you get a str
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
add a comment |
Because a number is a valid expression in Python, and it evaluates to itself (and its type is int). For example, if you input a rubbish string with a non-existing name (say, 'abcdefgh'), a NameError exception will be raised (the exception is raised while evaluating).
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Why does this happen?
x = eval(input("Enter a number: ")) is not the same thing as x = eval('input("Enter a number: ")')
The former first calls input(...), gets a string, e.g. '5' then evaluates it, that's why you get an int, in this manner:
>>> eval('5') # the str '5' is e.g. the value it gets after calling input(...)
5 # You get an int
While the latter (more aligned with what you were expecting), evaluates the expression 'input("Enter a number: ")'
>>> x = eval('input("Enter a number: ")')
Enter a number: 5
>>> x
'5' # Here you get a str
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
add a comment |
Why does this happen?
x = eval(input("Enter a number: ")) is not the same thing as x = eval('input("Enter a number: ")')
The former first calls input(...), gets a string, e.g. '5' then evaluates it, that's why you get an int, in this manner:
>>> eval('5') # the str '5' is e.g. the value it gets after calling input(...)
5 # You get an int
While the latter (more aligned with what you were expecting), evaluates the expression 'input("Enter a number: ")'
>>> x = eval('input("Enter a number: ")')
Enter a number: 5
>>> x
'5' # Here you get a str
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
add a comment |
Why does this happen?
x = eval(input("Enter a number: ")) is not the same thing as x = eval('input("Enter a number: ")')
The former first calls input(...), gets a string, e.g. '5' then evaluates it, that's why you get an int, in this manner:
>>> eval('5') # the str '5' is e.g. the value it gets after calling input(...)
5 # You get an int
While the latter (more aligned with what you were expecting), evaluates the expression 'input("Enter a number: ")'
>>> x = eval('input("Enter a number: ")')
Enter a number: 5
>>> x
'5' # Here you get a str
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
Why does this happen?
x = eval(input("Enter a number: ")) is not the same thing as x = eval('input("Enter a number: ")')
The former first calls input(...), gets a string, e.g. '5' then evaluates it, that's why you get an int, in this manner:
>>> eval('5') # the str '5' is e.g. the value it gets after calling input(...)
5 # You get an int
While the latter (more aligned with what you were expecting), evaluates the expression 'input("Enter a number: ")'
>>> x = eval('input("Enter a number: ")')
Enter a number: 5
>>> x
'5' # Here you get a str
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
edited Jun 19 '16 at 19:18
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
answered Jun 19 '16 at 19:12
bakkalbakkal
41.5k98286
41.5k98286
add a comment |
add a comment |
Because a number is a valid expression in Python, and it evaluates to itself (and its type is int). For example, if you input a rubbish string with a non-existing name (say, 'abcdefgh'), a NameError exception will be raised (the exception is raised while evaluating).
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
add a comment |
Because a number is a valid expression in Python, and it evaluates to itself (and its type is int). For example, if you input a rubbish string with a non-existing name (say, 'abcdefgh'), a NameError exception will be raised (the exception is raised while evaluating).
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
add a comment |
Because a number is a valid expression in Python, and it evaluates to itself (and its type is int). For example, if you input a rubbish string with a non-existing name (say, 'abcdefgh'), a NameError exception will be raised (the exception is raised while evaluating).
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
Because a number is a valid expression in Python, and it evaluates to itself (and its type is int). For example, if you input a rubbish string with a non-existing name (say, 'abcdefgh'), a NameError exception will be raised (the exception is raised while evaluating).
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
answered Jun 19 '16 at 19:12
Pavel GurkovPavel Gurkov
564413
564413
add a comment |
add a comment |
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maybe it is a dynamic type check when you use eval()?
– cssGEEK
Jun 19 '16 at 19:12
1
evaltreats the input like it was written in code, doingx = 3in code makes an integer, sox = eval("3")will also make x an integer, however letting the user enter arbitrary code as their input can be a huge problem, if they typed inopen(__file__,'w').close()it would delete the current executing file.– Tadhg McDonald-Jensen
Jun 19 '16 at 19:18