将 python 数据帧传递给对象并更改数据帧

Question

我是Python新手，我试图将参数（数据帧）传递给函数并通过读取Excel文件来更改参数（数据帧）的值。（假设我已经导入了所有必需的文件）

我注意到 python 在这里没有通过引用传递参数，并且我最终没有初始化/更改数据帧。

我读到 python 通过对象引用传递，而不是通过值或引用传递。但是，我不需要更改相同的数据框。

输出是：类'pandas.core.frame.DataFrame'>

from pandas import DataFrame as df
class Data:
   x = df

   @staticmethod
   def import_File(df_name , file):
       df_name  = pd.io.excel.read_excel(file.replace('"',''), sheetname='Sheet1', header=0, skiprows=None, skip_footer=0, index_col=None, parse_cols=None, parse_dates=True, date_parser=True, na_values=None, thousands=None, convert_float=True, has_index_names=None, converters=None, engine=None )


def inputdata():
    Data.import_File(Data.x,r"C:\Users\Data\try.xlsx")
    print(Data.x)

Answer 1

你似乎正在以艰难的方式做很多事情。我将尝试简化它，同时符合标准使用模式。

# Whatever imports you need
import pandas as pd


# Static variables and methods should generally be avoided.
# Change class and variable names to whatever is more suitable.
# Names should be meaningful when possible.
class MyData:

    # Load data in constructor. Could easily do this in another method.
    def __init__(self, filename):
        self.data = pd.io.excel.read_excel(filename, sheetname='Sheet1')


def inputData():
    # In my experience, forward slashes work just fine on Windows.
    # Create new MyData object using constructor
    x = MyData('C:/Users/Data/try.xlsx')

    # Access member variable from object
    print(x.data)

这是在方法而不是构造函数中加载的版本。

import pandas as pd


class MyData:

    # Constructor
    def __init__(self):
        # Whatever setup you need
        self.data = None
        self.loaded = False

    # Method with optional argument
    def loadFile(self, filename, sheetname='Sheet1')
        self.data = pd.io.excel.read_excel(filename, sheetname=sheetname)
        self.loaded = True


def inputData():
    x = MyData()
    x.loadFile('C:/Users/Data/try.xlsx')
    print(x.data)

    # load some other data, using sheetname 'Sheet2' instead of default
    y = MyData()
    y.loadFile('C:/Users/Data/tryagain.xlsx', 'Sheet2')
    # can also pass arguments by name in any order like this:
    # y.loadFile(sheetname='Sheet2', filename='C:/Users/Data/tryagain.xlsx')
    print(y.data)

    # x and y both still exist with different data.
    # calling x.loadFile() again with a different path will overwrite its data.

它不保存在原始代码中的原因是，为参数名称赋值永远不会更改 Python 中的原始变量。你可以做的是这样的：

# Continuing from the last code block

def loadDefault(data):
    data.loadFile('C:/Users/Data/try.xlsx')

def testReference():
    x = MyData()
    loadDefault(x)
    # x.data now has been loaded
    print(x.data)


# Another example

def setIndex0(variable, value):
    variable[0] = value

def testSetIndex0():
    v = ['hello', 'world']
    setIndex0(v, 'Good morning')
    # v[0] now equals 'Good morning'
    print(v[0])

但你不能这样做：

def setString(variable, value):
    # The only thing this changes is the value of variable inside this function.
    variable = value

def testSetString():
    v = 'Start'
    setString(v, 'Finish')
    # v is still 'Start'
    print(v)

如果您希望能够使用名称指定存储值的位置，则可以使用带有索引/键的数据结构。字典允许您使用键访问和存储值。

import pandas as pd


class MyData:

    # Constructor
    def __init__(self):
        # make data a dictionary
        self.data = {}

    # Method with optional argument
    def loadFile(self, storename, filename, sheetname='Sheet1')
        self.data[storename] = pd.io.excel.read_excel(filename, sheetname=sheetname)

    # Access method
    def getData(self, name):
        return self.data[name]


def inputData():
    x = MyData()
    x.loadFile('name1', 'C:/Users/Data/try.xlsx')
    x.loadFile('name2', 'C:/Users/Data/tryagain.xlsx', 'Sheet2')

    # access Sheet1
    print(x.getData('name1'))

    # access Sheet2
    print(x.getData('name2'))

如果您确实希望该函数是静态的，那么您根本不需要创建一个新类。创建类的主要原因是将其用作可重用结构，以通过特定于该数据的方法来保存数据。

import pandas as pd

# wrap read_excel to make it easier to use
def loadFile(filename, sheetname='Sheet1'):
    return pd.io.excel.read_excel(filename, sheetname=sheetname)

def inputData():
    x = loadFile('C:/Users/Data/try.xlsx')
    print(x)

    # the above is exactly the same as
    x = pd.io.excel.read_excel('C:/Users/Data/try.xlsx', sheetname='Sheet1')
    print(x)