Python脚本循环50次仅输出1行，需提取每次迭代的Period字段

核心问题原因 #

• 存储结果的代码被放在了for x in range(50):循环外部，循环执行50次后，只有最后一次生成的df被处理并追加到storage_df，所以最终输出仅1行。
• 每次循环中df变量会被重新赋值，之前循环生成的df直接被覆盖，无法保留用于后续存储。

修复后的完整代码 #

import pandas as pd
import numpy as np
import numpy_financial as npf
from datetime import date, datetime
from numpy import random

# 提前初始化列表，用于收集每次循环的目标数据
results_list = []

for x in range(50):
    interest=0.04125
    years=2
    payments_year=12
    mortgage=40000
    start_date=(date(2023, 2, 1))

    initial_pmt = -1 * npf.pmt(interest / 12, years * payments_year, mortgage)
    initial_ipmt = -1 * npf.ipmt(interest / payments_year, 1, years * payments_year, mortgage)
    initial_ppmt = -1 * npf.ppmt(interest / payments_year, 1, years * payments_year, mortgage)
    print(f'第{x+1}次迭代 - Initial Payment: {:,.2f}'.format(initial_pmt))
    print(f'第{x+1}次迭代 - Initial Interest: {:,.2f}'.format(initial_ipmt))
    print(f'第{x+1}次迭代 - Initial Principal Payment: {:,.2f}'.format(initial_ppmt))

    # 创建日期范围
    rng = pd.date_range(start_date, periods=years * payments_year, freq='MS')
    rng.name="Payment Date"

    # 初始化数据表
    df=pd.DataFrame(
        index=rng,
        columns= ['Org Total Payment',
                  'Total Payment',
                  'Interest',
                  'Principal',
                  'Additional Payment',
                  'Org Ending Balance',
                  'Ending Balance'], dtype='float')
    # 设置还款期为索引
    df.reset_index(inplace=True)
    df.index += 1
    df.index.name="Period"

    # 填充第一期数据
    period=1
    additional_pmt = np.random.randint(2100, 4500, size=len(df))

    initial_row_dict = {
        'Org Total Payment':initial_pmt,
        'Total Payment': initial_pmt + (additional_pmt),
        'Interest': initial_ipmt,
        'Principal':initial_ppmt,
        'Additional Payment': additional_pmt,
        'Org Ending Balance': mortgage - initial_ppmt,
        'Ending Balance': mortgage - initial_ppmt - (additional_pmt)
    }

    columns = list(initial_row_dict.keys())
    period_values = list(initial_row_dict.values())
    df.at[period, columns]= period_values

    # 填充后续期数数据
    for period in range(2, len(df) + 1):
        previous_total_payment = df.loc[period - 1, 'Total Payment']
        previous_principal = df.loc[period - 1, 'Principal']
        previous_org_ending_balance = df.loc[period - 1, 'Org Ending Balance']
        previous_ending_balance = df.loc[period - 1, 'Ending Balance']
        
        period_interest = previous_org_ending_balance * interest / payments_year
        period_principal = initial_pmt - period_interest
        additional_pmt = np.random.randint(2100, 4500) + 400
        org_ending_balance = previous_org_ending_balance - period_principal
        ending_balance = previous_ending_balance - period_principal - additional_pmt

        row_dict = {'Org Total Payment':initial_pmt,
                    'Total Payment': initial_pmt + (additional_pmt),
                    'Interest': period_interest,
                    'Principal': period_principal,
                    'Additional Payment': additional_pmt,
                    'Org Ending Balance': org_ending_balance,
                    'Ending Balance': ending_balance}
        columns = list(row_dict.keys())
        period_values = list(row_dict.values())
        df.at[period, columns]= period_values

    # 每次循环内提取当前结果的最后一行Period字段
    df_mask=df['Ending Balance']>=0
    filtered_df = df[df_mask].round(2)
    last_row = filtered_df.tail(1)
    # 仅保留Period列，加入结果列表
    results_list.append(last_row[['Period']].reset_index(drop=True))

# 合并所有结果为最终数据表
storage_df = pd.concat(results_list, ignore_index=True)
print(storage_df)
# 导出CSV时去除无用索引
storage_df.to_csv('allruns.csv', index=False)

关键修改点 #

• 将结果收集移入循环：每次循环处理完当前df后，立即提取目标数据并加入列表，避免数据被覆盖。
• 替换append为列表+concat：pd.DataFrame.append()已被标记为弃用，改用列表收集小数据块后合并，效率更高且符合规范。
• 按需保留字段：仅提取最后一行的Period字段，满足需求同时减少数据冗余。
• 添加迭代标识：打印信息时加入迭代次数，方便调试观察循环执行状态。
• 优化CSV导出：添加index=False避免导出的CSV多出无用索引列。

内容的提问来源于stack exchange，提问作者reenum