Python中的 pandas.eval()函数

此方法用于使用各种后端将Python表达式评估为字符串。它返回 ndarray、数值标量、DataFrame、Series。

Syntax : pandas.eval(expr, parser=’pandas’, engine=None, truediv=True, local_dict=None, global_dict=None, resolvers=(), level=0, target=None, inplace=False)

Arguments :

• expr : str or unicode. The expression to evaluate. This string cannot contain any Python
• parser : string, default ‘pandas’, {‘pandas’, ‘python’}.
• engine : string or None, default ‘numexpr’, {‘python’, ‘numexpr’}
• truediv : bool, optional, Whether to use true division, like in Python >= 3
• level : int, optional, The number of prior stack frames to traverse and add to the current scope. Most users will **not** need to change this parameter.

以下是上述方法的实现以及一些示例：

示例 1：

Python3

# importing package
import pandas
  
# evaluate the expressions given
# in form of string
print(pandas.eval("2+3"))
print(pandas.eval("2+3*(5-2)"))

输出 ：

5
11

示例 2：

Python3

# importing package
import pandas
  
# creating data
data = pandas.DataFrame({
      "Student": ["A", "B", "C", "D"], 
    "Physics": [89,34,23,56], 
    "Chemistry": [34,56,98,56], 
    "Math": [34,94,50,59]
    })
  
# view data
display(data)
  
# adding new column by existing 
# columns evaluation
data['Total']=pandas.eval("data.Physics+data.Chemistry+data.Math")
  
# view data
display(data)
  
# adding new column by existing 
# columns evaluation
pandas.eval("Avg=data.Total/3",target=data,inplace=True)
  
# view data
display(data)

输出 ：