Amazing Python 2: "exec/eval/repr"
1. exec:Executing command from string.
class PlayerBase():
player_name = None
def talk(self):
print self.player_name, ": It takes five."
class Kobe(PlayerBase):
def __init__(self):
self.player_name = "Kobe."
class TMac(PlayerBase):
def __init__(self):
self.player_name = "TMac"
input_name = "TMac"
cmd = "player = " + input_name + "()"
exec(cmd)
player.talk()
Output:
TMac : It takes five.
With "exec", objects of different class types can be created directly from strings without "switch-case"!
(In this way, do we still need to use the design pattern of "Simple Factory"?)
2. eval:
Calculating value from string.
>>> eval( ' 2 * 3 ' )
6
3. repr:
Acquiring string from value.
>>> dict = { "First" : 1, "Second" : 2 }
>>> string = repr(dict)
>>> string
"{'Second': 2, 'First': 1}"
>>> string
"rst': 1}"
4. eval & repr:
Converting between value and string, which is greatly suitable for transmission of high-level data structs (e.g., a dictionary) over socket!
>>> dict = { "First" : 1, "Second" : 2 }
>>> repr(dict)
"{'Second': 2, 'First': 1}"
>>> eval(repr(dict))
{'Second': 2, 'First': 1}
>>> eval(repr(dict)) == dict
True
See more at Chapter 15, 简明 Python 教程
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