函数前变量赋值

Question

我创建了一个包来使用 pandas 和 xlsxwriter 快速转换数据。 这工作得很好，我成功地完成了一些功能。但最近我碰壁了：

对于一些函数，我需要先定义变量，但它们不是基本类型（列表、元组、str 等），而是例如数据帧。我查看了全局变量，发现它们没有被推荐（并且不知道将它们放在哪里），我也查看了类，但我不知道如何使用它们来解决我的问题。我也尝试过创建一个空数据框，但在函数之后得到了一个空数据框。

我正在尝试使用 pandas 读取 .csv 或 .xlsx 的功能以及使用 Xlsxwriter 引擎进行保存的功能。 目标是尽可能少地更改代码以频繁和快速地转换数据（例如，我有像 Excel 中一样执行 LEFT、RIGHT 的函数，甚至是带有列号的 MIDDLE），并且在 main.py 中有一个简单而简短的代码。

这是我的代码的精简版，它使用 2 个 python 文件（main.py 和 format_operations.py）。我在有问题的地方添加了评论。 提前感谢您的帮助！

    """ 
    main.py
    """
    import format_operations as tbfrm #import another python file in the same folder
    import pandas as pd
    import numpy as np
    import xlsxwriter.utility

    #file settings
    file_full_path= "C:/Tests/big_data.xlsx"
    file_save_to= "C:/Tests/Xlsxwriter.xlsx"
    sheet_name_save_to= "Xlswriter"
    dfname = ??? #I need to create the variable but I don't know how
    tbfrm.FCT_universal_read(dfname,file_full_path) #CAN'T GET IT TO WORK

    #column operations and formatting
    columns_numeric = [3,6] # (with pandas) list of columns with number values by iloc number, starts at 0 which is column A in Excel
    tbfrm.FCT_columns_numeric(dfname,columns_numeric) #example of a WORKING function (if dfname is defined)

    #write with Xlsxwriter engine
    XLWRITER_DF = ??? #same problem as before, how to create the variable?
    workbookvarname = ??? #same here
    worksheetvarname = ??? # same here
    tbfrm.FCT_df_xlsxwriter(XLWRITER_DF,dfname,file_save_to,sheet_name_save_to,workbookvarname,worksheetvarname) #CAN'T GET IT TO WORK

    #### WORKING piece of code I want to execute after saving with Xlsxwriter engine ####
    worksheet.set_zoom(80)

    # Conditional formatting
    color_range_1 = "J1:J{}".format(number_rows+1)
    FORMAT1 = workbook.add_format({'bg_color': '#FFC7CE','font_color': '#9C0006'})
    FORMAT2 = workbook.add_format({'bg_color': '#C6EFCE','font_color': '#006100'})
    worksheet.conditional_format(color_range_1, {'type': 'bottom','value': '5','format': FORMAT1})
    worksheet.conditional_format(color_range_1, {'type': 'top','value': '5','format': FORMAT2})

其他文件：

    """ 
    format_operations.py
    """
    import pandas as pd
    import numpy as np
    import xlsxwriter.utility

    def FCT_universal_read(dfname,file_full_path):
        if ".xls" in file_full_path:
            dfname = pd.read_excel(file_full_path) #optional arguments:sheetname='Sheet1', header=0 , dtype=object to preserve values
        if ".csv" in file_full_path:
            dfname = pd.read_csv(file_full_path)

    # save file with XLSXWriter engine for additional options to pandas
    def FCT_df_xlsxwriter(XLWRITER_DF,dfname,file_save_to,sheet_name_save_to,workbookvarname,worksheetvarname):
        XLWRITER_DF = pd.ExcelWriter(file_save_to, engine='xlsxwriter')
        dfname.to_excel(XLWRITER_DF, sheet_name=sheet_name_save_to,encoding='utf-8')
        workbookvarname = XLWRITER_DF.book
        worksheetvarname = XLWRITER_DF.sheets[sheet_name_save_to]

    #format as numbers
    def FCT_columns_numeric(dfname,columns_numeric):
        for x in columns_numeric:
            dfname.iloc[:,x] = pd.to_numeric(dfname.iloc[:,x])

Answer 1

您的 FCT_universal_read 函数不应修改数据帧，而是返回一个新数据帧：

def FCT_universal_read(file_full_path):
    if file_full_path.split('.')[-1] == "xls":
        df = pd.read_excel(file_full_path) #optional arguments:sheetname='Sheet1', header=0 , dtype=object to preserve values
    if file_full_path.split('.')[-1] == "csv":
        df = pd.read_csv(file_full_path)
    return df

在你的主要，做：

dfname = tbfrm.FCT_universal_read(file_full_path)

FCT_df_xlsxwriter 的答案相同，你应该用 return 重写它，以便你可以这样做：

    XLWRITER_DF, workbookvarname,worksheetvarname =  tbfrm.FCT_df_xlsxwriter(dfname,file_save_to,sheet_name_save_to) 

要了解 python 如何处理您传递给函数的参数，您应该阅读以下博客文章：

https://jeffknupp.com/blog/2012/11/13/is-python-callbyvalue-or-callbyreference-neither/ https://robertheaton.com/2014/02/09/pythons-pass-by-object-reference-as-explained-by-philip-k-dick/

Answer 2

您需要更新FCT_universal_read 以便它返回您想要的数据框。无需在函数外定义dataframe，只需创建并返回即可

df = FCT_universal_read('/your/file/path')

def FCT_universal_read(file_full_path):
        if ".xls" in file_full_path:
            df = pd.read_excel(file_full_path) #optional arguments:sheetname='Sheet1', header=0 , dtype=object to preserve values
            return df
        if ".csv" in file_full_path:
            df = pd.read_csv(file_full_path)
            return df

Answer 3

非常感谢你们！我现在明白了逻辑:)！也感谢您的文档。

我成功地完成了这两个功能。我已经挣扎了几个小时。 我喜欢您使用的 .split 函数，它确保脚本只查看扩展名。

正如你所说，我更新了 FCT_xlsxwriter 和 FCT_universal_read。以下是已更正的两个函数：

    '''
    format_operations.py
    '''
    def FCT_universal_read(file_full_path):
        if "xls" in file_full_path.split('.')[-1]:
            dfname = pd.read_excel(file_full_path) #example: C:/Tests/Bigdata.xlsx
            return dfname
        if "csv" in file_full_path.split('.')[-1]:
            dfname = pd.read_csv(file_full_path)
            return dfname


    def FCT_df_xlsxwriter(dfname,file_save_to,sheet_name_save_to):
        XLWRITER_DF = pd.ExcelWriter(file_save_to, engine='xlsxwriter')
        dfname.to_excel(XLWRITER_DF, sheet_name=sheet_name_save_to,encoding='utf-8')
        workbook = XLWRITER_DF.book
        worksheet = XLWRITER_DF.sheets[sheet_name_save_to]
        return XLWRITER_DF,workbook,worksheet

我是这样调用这两个函数的：

    '''
    main.py
    '''

    import format_operations as tbfrm
    import pandas as pd
    import xlsxwriter.utility

    #settings
    file_full_path= "C:/Tests/big_data.xlsx"
    file_save_to= "C:/Tests/Xlsxwriter.xlsx"
    sheet_name_save_to= "Xlswriter"

    #functions
    FILE_DF = tbfrm.FCT_universal_read(file_full_path)
    XLWRITER_DF,workbook,worksheet = tbfrm.FCT_df_xlsxwriter(FILE_DF,file_save_to,sheet_name_save_to)