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Filename : _py.sh
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# -*- sh-basic-offset: 2 -*-
##
# Copyright (c) 2005-2017 Apple Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
##

find_cmd () {
  local cmd="$1"; shift;

  local path="$(type "${cmd}" 2>/dev/null | sed "s|^${cmd} is \(a tracked alias for \)\{0,1\}||")";

  if [ -z "${path}" ]; then
    return 1;
  fi;

  echo "${path}";
}

# Echo the major.minor version of the given Python interpreter.

py_version () {
  local python="$1"; shift;
  echo "$("${python}" -c "from distutils.sysconfig import get_python_version; print get_python_version()")";
}

#
# Test if a particular python interpreter is available, given the full path to
# that interpreter.
#
try_python () {
  local python="$1"; shift;

  if [ -z "${python}" ]; then
    return 1;
  fi;

  if ! type "${python}" > /dev/null 2>&1; then
    return 1;
  fi;

  local py_version="$(py_version "${python}")";
  if [ "$(echo "${py_version}" | sed 's|\.||')" -lt "25" ]; then
    return 1;
  fi;
  return 0;
}


#
# Detect which version of Python to use, then print out which one was detected.
#
# This will prefer the python interpreter in the PYTHON environment variable.
# If that's not found, it will check for "python2.7" and "python", looking for
# each in your PATH.
#
detect_python_version () {
  local v;
  local p;
  for v in "2.7" "2" ""
  do
    for p in         \
      "${PYTHON:=}"  \
      "python${v}"   \
      ;
    do
      if p="$(find_cmd "${p}")"; then
        if try_python "${p}"; then
          echo "${p}";
          return 0;
        fi;
      fi;
    done;
  done;
  return 1;
}


#
# Compare version numbers
#
cmp_version () {
  local  v="$1"; shift;
  local mv="$1"; shift;

  local vh;
  local mvh;
  local result;

  while true; do
     vh="${v%%.*}"; # Get highest-order segment
    mvh="${mv%%.*}";

    if [ "${vh}" -gt "${mvh}" ] 2>/dev/null; then
      result=1;
      break;
    fi;

    if [ "${vh}" -lt "${mvh}" ] 2>/dev/null; then
      result=0;
      break;
    fi;

    if [ "${v}" = "${v#*.}" ]; then
      # No dots left, so we're ok
      result=0;
      break;
    fi;

    if [ "${mv}" = "${mv#*.}" ]; then
      # No dots left, so we're not gonna match
      result=1;
      break;
    fi;

     v="${v#*.}";
    mv="${mv#*.}";
  done;

  return ${result};
}


#
# Detect which python to use, and store it in the 'python' variable, as well as
# setting up variables related to version and build configuration.
#
init_py () {
  # First, detect the appropriate version of Python to use, based on our version
  # requirements and the environment.  Note that all invocations of python in
  # our build scripts should therefore be '"${python}"', not 'python'; this is
  # important on systems with older system pythons (2.4 or earlier) with an
  # alternate install of Python, or alternate python installation mechanisms
  # like virtualenv.
  bootstrap_python="$(detect_python_version)";

  # Set the $PYTHON environment variable to an absolute path pointing at the
  # appropriate python executable, a standard-ish mechanism used by certain
  # non-distutils things that need to find the "right" python.  For instance,
  # the part of the PostgreSQL build process which builds pl_python.  Note that
  # detect_python_version, above, already honors $PYTHON, so if this is already
  # set it won't be stomped on, it will just be re-set to the same value.
  export PYTHON="$(find_cmd ${bootstrap_python})";

  if [ -z "${bootstrap_python:-}" ]; then
    echo "No suitable python found. Python 2.6 or 2.7 is required.";
    exit 1;
  fi;
}