eval SyntaxError: invalid syntax in python
Question:
I want to assign :
x0='123'
x1='123'
x2='123'
x3='123'
x4='123'
x5='123'
x6='123'
x7='123'
x8='123'
x9='123'
I write the code to express that i can get the output of a string 123
when input x1
or x8
.
for i in range(0,10):
eval("x"+str(i)+"='123'")
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
File "<string>", line 1
x0='123'
^
SyntaxError: invalid syntax
How i can do that way?
Do not ever use eval
(or exec
) on data that could possibly come from outside the program in any form. It is a critical security risk. You allow the author of the data to run arbitrary code on your computer. If you are here because you want to create multiple variables in your Python program following a pattern, you almost certainly have an XY problem. Do not create those variables at all – instead, use a list or dict appropriately.
Answers:
eval()
only allows for expressions. Assignment is not an expression but a statement; you’d have to use exec
instead.
Even then you could use the globals()
dictionary to add names to the global namespace and you’d not need to use any arbitrary expression execution.
You really don’t want to do this, you need to keep data out of your variable names and use a list or dictionary instead:
x = ['123'] * 10
would give you a list you can address as x[0]
, x[1]
, etc. without having to execute arbitrary expressions.
For dynamic execution of statements use the exec
function:
>>> exec('y = 3')
>>> y
3
eval
usage: eval(expression)
.
The expression
argument is parsed and evaluated as a Python expression.
e.g.:
>>> s = 3
>>> eval('s == 3')
True
>>> eval('s + 1')
4
>>> eval('s')
3
>>> eval('str(s) + "test"')
'3test'
You can you this expression.
eval('"x"+str(i)+"="+"123"')
I want to assign :
x0='123'
x1='123'
x2='123'
x3='123'
x4='123'
x5='123'
x6='123'
x7='123'
x8='123'
x9='123'
I write the code to express that i can get the output of a string 123
when input x1
or x8
.
for i in range(0,10):
eval("x"+str(i)+"='123'")
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
File "<string>", line 1
x0='123'
^
SyntaxError: invalid syntax
How i can do that way?
Do not ever use eval
(or exec
) on data that could possibly come from outside the program in any form. It is a critical security risk. You allow the author of the data to run arbitrary code on your computer. If you are here because you want to create multiple variables in your Python program following a pattern, you almost certainly have an XY problem. Do not create those variables at all – instead, use a list or dict appropriately.
eval()
only allows for expressions. Assignment is not an expression but a statement; you’d have to use exec
instead.
Even then you could use the globals()
dictionary to add names to the global namespace and you’d not need to use any arbitrary expression execution.
You really don’t want to do this, you need to keep data out of your variable names and use a list or dictionary instead:
x = ['123'] * 10
would give you a list you can address as x[0]
, x[1]
, etc. without having to execute arbitrary expressions.
For dynamic execution of statements use the exec
function:
>>> exec('y = 3')
>>> y
3
eval
usage: eval(expression)
.
The expression
argument is parsed and evaluated as a Python expression.
e.g.:
>>> s = 3
>>> eval('s == 3')
True
>>> eval('s + 1')
4
>>> eval('s')
3
>>> eval('str(s) + "test"')
'3test'
You can you this expression.
eval('"x"+str(i)+"="+"123"')