Python executes a string expression function (eval exec execfile) _python

After careful study, I learned three functions:
Eval: Evaluating an expression in a string
EXEC: Executing a statement in a string
ExecFile: Used to execute a file

It should be noted that EXEC is a statement, while Eval () and execfile () are built-in built-in functions.

Python 2.7.2 (Default, June, 15:08:59) [MSC v.1500 bit (Intel)] on Win32
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>>> x=1
>>> print eval ("x+1")
2
>>> exec "print" http://blog.leniy.org/ Python-eval-exec-execfile.html ' "
http://blog.leniy.org/python-eval-exec-execfile.html

At the same time, we sometimes use input to enter some data, such as

>>> input ("Please enter:")
Please input: 1+2**3
9

In fact, the input here is also the application of eval, which is equivalent to

>>> eval (raw_input ("Please enter:")
Please input: 1+2**3
9