Python文件操作：如何避免重复写入并跳过已追加内容？

问题分析 #

你的代码当前存在两个核心问题：

1. 每次运行会读取文件中所有内容（包括之前追加的结果行），结果行无法转为整数会触发报错；
2. 未记录已处理的请求，导致重复运行时会重复写入相同的处理结果。

下面提供两种可行的实现方案：

方案一：单文件分隔符区分请求与结果 #

通过在文件中加入固定分隔符，将原始请求行和处理结果行分开，读取时仅处理分隔符前的请求，同时解析结果行标记已处理的请求，避免重复写入。

修正后的代码：

kitty = 500
# 定义分隔符，用于区分请求和结果区域
SEPARATOR = "--- REQUESTS END ---"

# 1. 读取文件，分离原始请求和已有处理结果
requests = []
existing_results = []
try:
    with open("loan_requests.txt", "r") as file:
        lines = file.readlines()
        separator_found = False
        for line in lines:
            stripped_line = line.strip()
            # 找到分隔符后，后续行均为结果行
            if stripped_line == SEPARATOR:
                separator_found = True
                continue
            if not separator_found:
                # 仅处理数字格式的请求行
                try:
                    req = int(stripped_line)
                    requests.append(req)
                except ValueError:
                    continue
            else:
                existing_results.append(line)
except FileNotFoundError:
    # 如果文件不存在，初始化请求列表（可根据需求调整）
    requests = [100, 200, 300, 0]

# 2. 从已有结果中提取已处理的请求金额
processed_requests = []
for line in existing_results:
    if "Request of" in line or "Outstanding Request:" in line:
        # 解析结果行中的请求金额
        for part in line.split():
            if part.isdigit():
                processed_requests.append(int(part))
                break

# 3. 处理未被处理过的请求
new_results = []
for req in requests:
    if req == 0:  # 原逻辑中的请求结束标记
        break
    if req in processed_requests:
        continue  # 跳过已处理的请求

    # 处理请求的核心逻辑（修正原代码的计算错误）
    if req <= kitty and kitty > 0:
        kitty -= req
        print(f"{req} - Paid!")
        new_results.append(f"Request of {req} paid in full.\n")
    elif req > kitty and kitty > 0:
        paid_amount = kitty
        kitty -= req
        print(f"{req} Request cannot be processed in full (Insufficient funds available). Amount paid: {paid_amount}")
        new_results.append(f"Request of {req} could not be paid in full. Partial payment of {paid_amount} made.\n")
    elif req > kitty and kitty <= 0:
        print(f"Request of {req} is UNPAID!")
        new_results.append(f"Outstanding Request:{req}\n")

# 4. 重新写入文件：请求行 + 分隔符 + 已有结果 + 新结果
with open("loan_requests.txt", "w") as file:
    # 写入原始请求行
    for req in requests:
        file.write(f"{req}\n")
    # 写入分隔符
    file.write(f"{SEPARATOR}\n")
    # 写入已有结果
    file.writelines(existing_results)
    # 写入新结果
    file.writelines(new_results)

方案说明 #

• 用SEPARATOR标记请求区域的结束，读取时仅处理该标记之前的数字行；
• 解析已有结果行提取已处理的请求金额，确保同一请求不会被重复处理；
• 修正了原代码中loan = int(item) + kitty的计算错误，改为正确的paid_amount = kitty；
• 处理文件不存在的情况，初始化默认请求列表（可根据实际需求调整）。

方案二：分离请求与结果到不同文件 #

将原始请求和处理结果分别存储到两个文件，逻辑更清晰，避免解析结果行的复杂度：

kitty = 500
REQUEST_FILE = "loan_requests.txt"
RESULT_FILE = "payment_results.txt"

# 1. 读取原始请求
try:
    with open(REQUEST_FILE, "r") as f:
        requests = [int(line.strip()) for line in f if line.strip().isdigit()]
except FileNotFoundError:
    requests = [100, 200, 300, 0]

# 2. 读取已有结果，提取已处理的请求
processed_requests = []
try:
    with open(RESULT_FILE, "r") as f:
        for line in f:
            if "Request of" in line or "Outstanding Request:" in line:
                for part in line.split():
                    if part.isdigit():
                        processed_requests.append(int(part))
                        break
except FileNotFoundError:
    pass

# 3. 处理未处理的请求
new_results = []
for req in requests:
    if req == 0:
        break
    if req in processed_requests:
        continue

    if req <= kitty and kitty > 0:
        kitty -= req
        print(f"{req} - Paid!")
        new_results.append(f"Request of {req} paid in full.\n")
    elif req > kitty and kitty > 0:
        paid_amount = kitty
        kitty -= req
        print(f"{req} Request cannot be processed in full (Insufficient funds available). Amount paid: {paid_amount}")
        new_results.append(f"Request of {req} could not be paid in full. Partial payment of {paid_amount} made.\n")
    elif req > kitty and kitty <= 0:
        print(f"Request of {req} is UNPAID!")
        new_results.append(f"Outstanding Request:{req}\n")

# 4. 将新结果追加到结果文件
with open(RESULT_FILE, "a") as f:
    f.writelines(new_results)

方案说明 #

• 原始请求仅存储在loan_requests.txt中，不会被修改；
• 处理结果追加到payment_results.txt，每次运行仅读取该文件标记已处理的请求；
• 逻辑更简洁，避免了重新写入整个请求文件的操作。

内容的提问来源于stack exchange，提问作者Dinko Spahija