解决 pip install -r requirements.txt 报错: Could not find a version that satisfies the requirement pyminifier~=2.1

在使用 pip install -r requirements.txt 安装依赖库时，你可能会遇到以下报错：

pip install -r requirements.txt
WARNING: Ignoring invalid distribution -ip (d:\anaconda\lib\site-packages)
WARNING: Ignoring invalid distribution -ip (d:\anaconda\lib\site-packages)
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:1129)'))': /simple/pyminifier/
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:1129)'))': /simple/pyminifier/
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:1129)'))': /simple/pyminifier/
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:1129)'))': /simple/pyminifier/
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:1129)'))': /simple/pyminifier/
Could not fetch URL https://pypi.org/simple/pyminifier/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pyminifier/ (Caused by SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1129)'))) - skipping
ERROR: Could not find a version that satisfies the requirement pyminifier~=2.1 (from versions: none)
ERROR: No matching distribution found for pyminifier~=2.1
WARNING: Ignoring invalid distribution -ip (d:\anaconda\lib\site-packages)
WARNING: Ignoring invalid distribution -ip (d:\anaconda\lib\site-packages)
WARNING: Ignoring invalid distribution -ip (d:\anaconda\lib\site-packages)

这个错误可能是由于网络连接或 SSL 证书问题导致的。你可以尝试以下步骤来解决问题：

1. 确保你的网络连接正常，并且可以访问 https://pypi.org/ 网站。
2. 尝试升级 pip 工具： 在命令行中执行 pip install --upgrade pip。
3. 尝试直接安装 pyminifier 库： 使用以下命令安装 pyminifier 库：pip install pyminifier.

如果以上步骤不起作用，请尝试使用 pip 的 --trusted-host 选项来忽略 SSL 证书问题。例如：

pip install --trusted-host pypi.org --trusted-host files.pythonhosted.org pyminifier

通过这些步骤，你应该能够成功解决问题并安装所需的库。