Python 无法安装带有pip 21.0.1 SSLEOFError的任何软件包

我正在Ubuntu1604上使用python 3.7和PIP21.0.1。我无法安装任何有此错误的python包

yc_qian@NiBaBa:~$ pip install pyopenssl
Defaulting to user installation because normal site-packages is not writeable
Looking in indexes: https://pypi.tuna.tsinghua.edu.cn/simple
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))': /simple/pyopenssl/
WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))': /simple/pyopenssl/
WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))': /simple/pyopenssl/
WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))': /simple/pyopenssl/
WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))': /simple/pyopenssl/
Could not fetch URL https://pypi.tuna.tsinghua.edu.cn/simple/pyopenssl/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.tuna.tsinghua.edu.cn', port=443): Max retries exceeded with url: /simple/pyopenssl/ (Caused by SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))) - skipping
ERROR: Could not find a version that satisfies the requirement pyopenssl
ERROR: No matching distribution found for pyopenssl
Could not fetch URL https://pypi.tuna.tsinghua.edu.cn/simple/pip/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.tuna.tsinghua.edu.cn', port=443): Max retries exceeded with url: /simple/pip/ (Caused by SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1076)'))) - skipping

我在上发现了类似的问题，但不知道如何解决。我还尝试降级pip，但该命令也使用pip，因此它遇到了相同的错误

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我怎样才能解决这个问题呢？

根据费利克斯提到的答案，我通过

unset http_proxy https_proxy

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在我的机器上运行Fiddler时，我收到了类似的错误。如果您正在运行它，请尝试将其关闭。@FelixEklöf No fiddler，我确实运行了VPN，但如果我关闭它并再次尝试安装，则没有任何区别。请检查以下答案：