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PythonNote034---把字符串当做代码执行


Intro

有时候,需要把字符串当做代码执行,看个例子

getattr

Get a named attribute from an object; getattr(x, ‘y’) is equivalent to x.y

import pandas as pd
df=pd.DataFrame({"x":[1,2,3]})

getattr(df,"x").count()

3

getattr(df,“x”)相当于df.x

如果想执行df.x*2怎么弄?

eval

eval("df.x*2")

0    2
1 4
2 6
Name: x, dtype: int64

如果想做赋值操作,可行吗?

eval("series = df.x*2")

Traceback (most recent call last):


File "D:\code\anaconda\lib\site-packages\IPython\core\interactiveshell.py", line 2961, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)


File "<ipython-input-16-8a3ac8db3859>", line 1, in <module>
eval("series = df.x*2")


File "<string>", line 1
series = df.x*2
^
SyntaxError: invalid syntax

不支持赋值操作

exec

exe_str = """
series1 = df.x*2
series2 = df.x*3
"""
exec(exe_str)

series1

0    2
1 4
2 6
Name: x, dtype: int64

当exe_str有字符串变量,这个方法就比较好用,代码改动会小一些

exec("print(%s.count())"%"series1")

3

简单的分析,可以尝试用用这方法

                                2022-01-13 于南京市江宁区九龙湖


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