Travis CI: "Unable to locate package python-opencv" Python 2.7 - python-2.7

Question

On a normal non-virtualenv Ubuntu machine I can run:
sudo apt-get install python-opencv
And then from Python 2.7 I can run import cv2. Success!
But when I try to do the very same thing in my .travis.yml file for automated testing, I get the error:
E: Unable to locate package python-opencv
How can I get apt-get to locate python-opencv in my Travis-CI build?
I've tried the following; all were unsuccessful:
From https://askubuntu.com/questions/339217/, I tried appending these lines to /etc/apt/sources.list:
echo "deb http://de.archive.ubuntu.com/ubuntu precise main restricted universe" | sudo tee -a /etc/apt/sources.list
echo "deb-src http://de.archive.ubuntu.com/ubuntu precise restricted main multiverse universe" | sudo tee -a /etc/apt/sources.list
echo "deb http://de.archive.ubuntu.com/ubuntu precise-updates main restricted universe" | sudo tee -a /etc/apt/sources.list
echo "deb-src http://de.archive.ubuntu.com/ubuntu precise-updates restricted main multiverse universe" | sudo tee -a /etc/apt/sources.list
From here I tried adding these lines right before:
sudo apt-get install python-software-properties
sudo add-apt-repository python-opencv
Following this, with updated method from here, I tried using this instead of 2.7:
python:
- "2.7_with_system_site_packages"
(My full .travis.yml file is here.)
Update
Burhan Khalid's answer did get OpenCV installed, so the error went away. However, then when I tried find the package using import cv2 it still couldn't find it, because the Travis-CI build machine is wrapped in a virtualenv. So we can't access packages outside of our hermetically-sealed build environment.
So I build from source. (References: here, here and here)
Here's how to do it in the .travis.yml file:
env:
global:
# Dependencies
- DEPS_DIR="`readlink -f $TRAVIS_BUILD_DIR/..`"
- OPENCV_BUILD_DIR=$DEPS_DIR/opencv/build
And then, in the before_install section:
- travis_retry git clone --depth 1 https://github.com/Itseez/opencv.git $DEPS_DIR/opencv
- mkdir $OPENCV_BUILD_DIR && cd $OPENCV_BUILD_DIR
- |
if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then
cmake -DBUILD_TIFF=ON -DBUILD_opencv_java=OFF -DWITH_CUDA=OFF -DENABLE_AVX=ON -DWITH_OPENGL=ON -DWITH_OPENCL=ON -DWITH_IPP=ON -DWITH_TBB=ON -DWITH_EIGEN=ON -DWITH_V4L=ON -DBUILD_TESTS=OFF -DBUILD_PERF_TESTS=OFF -DCMAKE_BUILD_TYPE=RELEASE -DCMAKE_INSTALL_PREFIX=$(python -c "import sys; print(sys.prefix)") -DPYTHON_EXECUTABLE=$(which python) -DPYTHON_INCLUDE_DIR=$(python -c "from distutils.sysconfig import get_python_inc; print(get_python_inc())") -DPYTHON_PACKAGES_PATH=$(python -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())") ..
else
cmake -DBUILD_TIFF=ON -DBUILD_opencv_java=OFF -DWITH_CUDA=OFF -DENABLE_AVX=ON -DWITH_OPENGL=ON -DWITH_OPENCL=ON -DWITH_IPP=ON -DWITH_TBB=ON -DWITH_EIGEN=ON -DWITH_V4L=ON -DBUILD_TESTS=OFF -DBUILD_PERF_TESTS=OFF -DCMAKE_BUILD_TYPE=RELEASE -DCMAKE_INSTALL_PREFIX=$(python3 -c "import sys; print(sys.prefix)") -DPYTHON_EXECUTABLE=$(which python3) -DPYTHON_INCLUDE_DIR=$(python3 -c "from distutils.sysconfig import get_python_inc; print(get_python_inc())") -DPYTHON_PACKAGES_PATH=$(python3 -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())") ..
fi
- make -j4
- sudo make install
- echo "/usr/local/lib" | sudo tee -a /etc/ld.so.conf.d/opencv.conf
- sudo ldconfig
- echo "PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig" | sudo tee -a /etc/bash.bashrc
- echo "export PKG_CONFIG_PATH" | sudo tee -a /etc/bash.bashrc
- export PYTHONPATH=$OPENCV_BUILD_DIR/lib/python3.3/site-packages:$PYTHONPATH

Answer 1

After:
sudo add-apt-repository python-opencv
You need
sudo apt-get update
So that the new repository information is correctly updated; before you can add packages from that repository.