Why is Python's eval() rejecting this multiline string, and how can I fix it?

Question

I am attempting to eval the following tab-indented string:

'''for index in range(10):
        os.system("echo " + str(index) + "")
'''

I get, "There was an error: invalid syntax , line 1"

What is it complaining about? Do I need to indent to match the eval() statement, or write it to a string file or temp file and execute that, or something else?

Thanks,

Answer 1

eval evaluates stuff like 5+3

exec executes stuff like for ...

>>> eval("for x in range(3):print x")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1
    for x in range(3):print x
      ^
SyntaxError: invalid syntax
>>> exec("for x in range(3):print x")
0
1
2
>>> eval('5+3')
8

Answer 2

To use such statements with eval you should convert them to code object first, using compile:

In [149]: import os

In [150]: cc = compile('''for index in range(10):
    os.system("echo " + str(index) + "")''','<string>','single')

In [154]: eval cc
--------> eval(cc)
0
Out[154]: 0
1
Out[154]: 0
2
Out[154]: 0
3
Out[154]: 0
4

In [159]: cc = compile("2+2", '<string>', 'single')  # works with simple expressions too 

In [160]: eval cc
--------> eval(cc)
Out[160]: 4

Answer 3

We evaluate (eval) expressions, and execute (exec) statements.

See: Expression Versus Statement.

Expression: Something which evaluates to a value. Example: 1+2/x
Statement: A line of code which does something. Example: GOTO 100