当你看到这个错误信息“ImportError: No module named flask”时，这意味着你的Python环境中没有安装Flask模块，Flask是一个轻量级的Web应用框架，它可以让你快速地构建Web应用程序，为了解决这个问题，你需要按照以下步骤在Python环境中安装Flask模块。

1、检查Python版本

你需要确保你的Python环境是2.7.x或3.4以上的版本，因为Flask 0.10及以后的版本不再支持Python 2.6和2.7，你可以通过在命令行中输入以下命令来查看你的Python版本：

python version

如果你的Python版本低于3.4，建议你升级到最新的稳定版本，你可以访问Python官网（https://www.python.org/downloads/）下载并安装最新版本的Python。

2、安装pip

Flask模块是通过pip（Python包管理器）进行安装的，你需要确保你的Python环境中已经安装了pip，你可以通过在命令行中输入以下命令来检查pip是否已经安装：

pip version

如果你还没有安装pip，你可以访问pip官网（https://pip.pypa.io/en/stable/installing/）下载并安装。

3、安装Flask

现在你已经确保了你的Python环境和pip都已经就绪，接下来就可以安装Flask模块了，在命令行中输入以下命令：

pip install Flask

等待安装完成后，你就可以在你的Python代码中导入Flask模块了。

from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
    return 'Hello, World!'
if __name__ == '__main__':
    app.run()

4、使用虚拟环境

为了避免不同项目之间的依赖冲突，建议你使用虚拟环境（virtualenv）来管理你的Python项目，虚拟环境可以为每个项目创建一个独立的Python运行环境，这样你可以为每个项目安装不同的依赖包，要使用虚拟环境，请按照以下步骤操作：

确保你已经安装了virtualenv，如果没有，可以通过以下命令安装：

pip install virtualenv

在你的项目目录下创建一个虚拟环境。

virtualenv myproject_env

接下来，激活虚拟环境，在Windows上，输入以下命令：

myproject_envScriptsactivate

在Linux或Mac上，输入以下命令：

source myproject_env/bin/activate

现在，你可以在虚拟环境中安装Flask和其他依赖包了。

pip install Flask gunicorn httpie requests blinker itsdangerous Jinja2 Werkzeug MarkupSafe click waitress passlib getpass PyYAML configparser urllib3 chardet idna cryptography pyOpenSSL certifi requests[security] twilio requests_oauthlib pythondateutil pytz boto3 googleapipythonclient googleauthhttplib2 googleauthoauthlib googleauthurllib3 gspread oauth2client pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib poplib kazoo cloudpickle msgpackpython simplejson cffi cryptography pyOpenSSL ndghttpsclient pyasn1 rsa pycrypto mock futures backports mockredis six mimetypes email idna chardet dnspython urllib3 netifaces ipaddress ftplib ndghttpsclient pyparsing imapclient imaplib smtplib pop