Three functions were learned after careful study:
eval:Calculates an expression in a string.
exec:Execute the statement in the string.
execfile: Used to execute a file.
Note that exec is a statement, while eval() and execfile() are built-in built-in functions.
Python 2.7.2 (default, Jun 12 2011, 15:08:59) [MSC v.1500 32 bit (Intel)] on win32
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>>> x=1
>>> print eval("x+1")
2
>>> exec "print '/'"
/
>>>
At the same time, we sometimes use input to enter some data, such as
>>> input("Please enter:")
Please enter:1+2**3
9
>>>
In fact, the input here is also an application of eval, equivalent to the
>>> eval(raw_input("Please enter:"))
Please enter:1+2**3
9
>>>