python - 奇怪的 If、Elif、Else 行为

Question

如果我单独使用以下任何条件，它就会按预期工作。 (有关所有条件，请参阅更大的代码块)。当我期望 (df['ColumnName'] == 'This Value').any(): 触发时，我确实会打印以下异常。

打印异常 'ColumName2' 这会打印 3 次，这样就告诉我满足了其中一个条件，它只是没有触发:$

独立工作

if filename.endswith('.csv'):
    print 'File is CSV'        
    df = pd.read_csv(os.path.join(root,filename), skip_blank_lines=True)
    try:
        if (df['ColumnName'] == 'This Value').any():
           final_df = df.drop(df.ix[df['ColumnName'] == 'This Value'].index)
           data = final_df.sort(ascending=True)
           data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")
    except Exception as e:
        print e

但是当在更大的 if、elif、else 中使用时，似乎都不起作用(甚至 else 也没有被命中)。语法似乎是正确的，而且我在 StackOverflow 上看到的答案似乎都没有涵盖这一点。没有一个条件是相同的，所以没有看到任何问题，我不完全确定是什么导致了问题。

较大的 if、elif、else

if filename.endswith('.csv'):
    df = pd.read_csv(os.path.join(root,filename), skip_blank_lines=True)
        try:
            if (df['ColumnName'] == 'That Value').any():
                print 'ColumnName and "That Value"'
                final_df = df.drop(df.ix[df['ColumnName'] == 'This Value'].index)
                data = final_df.sort(ascending=True)
                data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")

            elif (df['ColumnName2'] == 'This Value').any():
                print 'ColumnName2 This Value'
                final_df = df.drop(df.ix[df['ColumnName2'] == 'This Value'].index)
                data = final_df.sort(ascending=True)
                data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")

            elif ((df['ColumnName2']=='That Value')).any():
                print 'ColumnName2 That Value'
                final_df = df[df['Dst Port'] != 'Any']
                data = final_df.sort(ascending=True)
                data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")

            elif ((df['ColumnName']=='This Value')).any():
                print 'ColumnName This Value'
                final_df = df[df['Service'] != 'Any']
                data = final_df.sort(ascending=True)
                data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")

            else:
                print 'No Filtering Applied'
                data = df.sort(ascending=True)
                data.to_csv(os.path.join(root, "Edit.csv"), index=False, na_rep="NA")
         except Exception as e:
             print e

修复感谢 AnandSKumars 评论

if filename.endswith('.csv'):
    try:
        df = pd.read_csv(os.path.join(root,filename), skip_blank_lines=True)
        if 'ColumnName' in df and (df['ColumnName'] == 'This Value').That Value():
            print 'Service and This Value'
            final_df = df.drop(df.ix[df['ColumnName'] == 'This Value'].index)
            data = final_df.sort(ascending=True)
            with open(os.path.join(root,'Edit.csv'), 'a') as f:
                data.to_csv(f, index=False, na_rep="NA")
            os.remove(os.path.join(root, filename))

        elif 'ColumnName2' in df and (df['ColumnName2'] == 'This Value').That Value():
            print 'ColumnName2 and This Value'
            final_df = df.drop(df.ix[df['ColumnName2'] == 'This Value'].index)
            data = final_df.sort(ascending=True)
            with open(os.path.join(root,'Edit.csv'), 'a') as f:
                data.to_csv(f, index=False, na_rep="NA")
            os.remove(os.path.join(root, filename))

        elif 'ColumnName2' in df and ((df['ColumnName2']=='That Value')).That Value():
            print 'ColumnName2 and That Value'
            final_df = df[df['ColumnName2'] != 'That Value']
            data = final_df.sort(ascending=True)
            with open(os.path.join(root,'Edit.csv'), 'a') as f:
                data.to_csv(f, index=False, na_rep="NA")
            os.remove(os.path.join(root, filename))

        elif 'ColumnName' in df and ((df['ColumnName']=='That Value')).That Value():
            print 'Service and That Value'
            final_df = df[df['ColumnName'] != 'That Value']
            data = final_df.sort(ascending=True)
            with open(os.path.join(root,'Edit.csv'), 'a') as f:
                data.to_csv(f, index=False, na_rep="NA")
            os.remove(os.path.join(root, filename))

        else:
            os.remove(os.path.join(root, filename))
    except Exception as e:
        print e

Answer 1

问题很可能是您有一些 csv 文件，但该 csv 文件中没有某些列。因此，将其读入数据帧后，当您尝试执行 df['ColumnName'] 时，会出现错误 - KeyError: 'ColumnName' 。这表明 DataFrame 中不存在 'ColumnName'。

但是一旦发生错误，它就会被 try..except block 捕获，因此不会出现任何其他 if 或 elif 条件火灾，因此您看不到输出。

如果您只想满足其中一个条件，那么您可以检查您尝试获取的列是否是 df 的一部分。示例-

if 'ColumnName' in df and (df['ColumnName'] == 'That Value').any():

其他 if 条件也类似。