Python列表添加字典元素时所有已有元素被覆盖的问题

问题 #

我尝试创建一个字典列表，这本应非常简单。我的代码可以正确添加新元素，但同时会将列表中所有已有的元素更新为相同的值。我忽略了什么？

原代码：

while y < search_repo_count:
    search_repo_name = search_results[n]["items"][y]["repository"]["name"]

    if team_repo_name == search_repo_name:
        print("Search Repo Name: " + search_repo_name + " Team Repo Name: " + team_repo_name + " y: " + str(y) + " z: " + str(z))
        search_match["repo_name"] = search_repo_name
        search_match["repo_url"] = search_results[n]["items"][y]["repository"]["html_url"]
        search_match["result_url"] = search_results[n]["items"][y]["html_url"]

        print(search_match)  # 这里输出符合预期

        final_output.append(search_match)  # 这里会插入新的search_match，但同时把列表里所有已有元素也改成这个值

        print(final_output)
        z = z + 1
    else:
        print("No Match")

    y = y + 1

运行结果：
repo_abc被正常插入final_output，repo_def作为新搜索值被插入时，之前的值也被覆盖成了repo_def。我期望第一个值保持不变，只添加新值作为新记录。

Search Repo Name: repo_abc Team Repo Name: repo_abc y: 7 z: 1
{'repo_name': 'repo_abc', 'repo_url': 'https://github.aexp.com/this-org/repo_abc', 'result_url': 'https://github.aexp.com/this-org/repo_abc/blob/f7bd013c7d72136dfb70a7ed4ae07a947768e0bd/src/main/java/com/aexp/team-a/nmi/NMICalculator.scala'}
[{'repo_name': 'repo_abc', 'repo_url': 'https://github.aexp.com/this-org/repo_abc', 'result_url': 'https://github.aexp.com/this-org/repo_abc/blob/f7bd013c7d72136dfb70a7ed4ae07a947768e0bd/src/main/java/com/aexp/team-a/nmi/NMICalculator.scala'}, {'repo_name': 'repo_abc', 'repo_url': 'https://github.aexp.com/this-org/repo_abc', 'result_url': 'https://github.aexp.com/this-org/repo_abc/blob/f7bd013c7d72136dfb70a7ed4ae07a947768e0bd/src/main/java/com/aexp/team-a/nmi/NMICalculator.scala'}]
...
Search Repo Name: repo_def Team Repo Name: repo_def y: 11 z: 2
{'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh'}
[{'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh'}, {'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh'}, {'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh'}]

Search Repo Name: repo_def Team Repo Name: repo_def y: 12 z: 3
{'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh_org'}
[{'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh_org'}, {'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh_org'}, {'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh_org'}, {'repo_name': 'repo_def', 'repo_url': 'https://github.aexp.com/this-org/repo_def', 'result_url': 'https://github.aexp.com/this-org/repo_def/blob/58769c59d6c1af2457b43dfaaf21c4ba2fb22594/ob-crmd-myca/scripts/myca_ob_ext.sh_org'}]

我还试过用final_output[z] = search_match和final_output.insert(n, search_match)更新列表，结果一样；把final_output改成字典也没用。

解决方法 #

问题出在字典是可变对象，你一直在复用同一个search_match字典。每次修改它的键值对时，列表里之前添加的所有引用都会指向这个同一个字典，所以所有元素都会跟着变。

要解决这个问题，每次匹配到新结果时，都要创建一个新的字典，而不是修改同一个旧字典。修改后的代码如下：

while y < search_repo_count:
    search_repo_name = search_results[n]["items"][y]["repository"]["name"]

    if team_repo_name == search_repo_name:
        print("Search Repo Name: " + search_repo_name + " Team Repo Name: " + team_repo_name + " y: " + str(y) + " z: " + str(z))
        # 每次循环创建新字典，而不是复用旧的
        search_match = {
            "repo_name": search_repo_name,
            "repo_url": search_results[n]["items"][y]["repository"]["html_url"],
            "result_url": search_results[n]["items"][y]["html_url"]
        }

        print(search_match)

        final_output.append(search_match)

        print(final_output)
        z = z + 1
    else:
        print("No Match")

    y = y + 1

这样每次添加到列表里的都是独立的新字典，修改新字典不会影响之前已经添加的元素。

内容的提问来源于stack exchange，提问作者fiffer1