use python 3 in Docker container

Dockerfile

@@ -22,6 +22,7 @@ RUN apt-get update && apt-get install -y \
     libtool \
     libtool-bin \
     libusb-1.0-0 \
+    locales  \
     make \
     ncurses-dev \
     network-manager \
@@ -40,6 +41,18 @@ RUN apt-get update && apt-get install -y \
     wget \
     wireless-tools
 
+RUN sed -i -e 's/# en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen && locale-gen
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US:en
+ENV LC_ALL en_US.UTF-8
+
+RUN curl -L https://github.com/pyenv/pyenv-installer/raw/master/bin/pyenv-installer | bash
+
+ENV PATH="/root/.pyenv/bin:/root/.pyenv/shims:${PATH}"
+RUN pyenv install 3.7.3
+RUN pyenv global 3.7.3
+RUN pyenv rehash
+
 RUN pip install --upgrade pip==18.0
 
 COPY requirements.txt /tmp/