Python requires

It is possible to reuse python code existing in other conanfile.py recipes with the python_requires functionality, doing something like:

from conans import ConanFile

class Pkg(ConanFile):
    python_requires = "pyreq/0.1@user/channel"

    def build(self):
        v = self.python_requires["pyreq"].module.myvar # myvar defined in pyreq's conanfile.py
        f = self.python_requires["pyreq"].module.myfunct() # myfunct defined in pyreq's conanfile.py
        self.output.info("%s,%s" % (v, f))

See this section: Python requires: reusing python code in recipes

Output and Running

Output contents

Use the self.output to print contents to the output.

self.output.success("This is a good, should be green")
self.output.info("This is a neutral, should be white")
self.output.warn("This is a warning, should be yellow")
self.output.error("Error, should be red")
self.output.rewrite_line("for progress bars, issues a cr")

Check the source code. You might be able to produce different outputs with different colors.

Running commands

run(self, command, output=True, cwd=None, win_bash=False, subsystem=None, msys_mingw=True,
    ignore_errors=False, run_environment=False, with_login=True):

self.run() is a helper to run system commands and throw exceptions when errors occur, so that command errors do not pass unnoticed. It is just a wrapper for subprocess.call().

When the environment variable CONAN_PRINT_RUN_COMMANDS is set to true (or its equivalent print_run_commands conan.conf configuration variable, under [general]) then all the invocations of self.run() will print to output the command to be executed.

The command can be specified as a string which is passed to the system shell. Alternatively it can be specified as a sequence of strings, the first of which is interpreted as the name of the program to be executed and the remaining ones are passed as arguments. Unless you are relying on shell-specific features such as redirection or command substitution, providing a sequence of strings is generally preferred as it allows Conan to take care of any required escaping and quoting of arguments (e.g. to permit spaces in file names).

Optional parameters:

output (Optional, Defaulted to True) When True it will write in stdout.: You can pass any stream that accepts a write method like a six.StringIO():

from six import StringIO  # Python 2 and 3 compatible
mybuf = StringIO()
self.run("mycommand", output=mybuf)
self.output.warn(mybuf.getvalue())

cwd (Optional, Defaulted to . current directory): Current directory to run the command.
win_bash (Optional, Defaulted to False): When True, it will run the configure/make commands inside a bash.
subsystem (Optional, Defaulted to None will autodetect the subsystem): Used to escape the command according to the specified subsystem.
msys_mingw (Optional, Defaulted to True) If the specified subsystem is MSYS2, will start it in MinGW mode (native windows development).
ignore_errors (Optional, Defaulted to False). This method raises an exception if the command fails. If ignore_errors=True, it will not raise an exception. Instead, the user can use the return code to check for errors.
run_environment (Optional, Defaulted to False). Applies a RunEnvironment, so the environment variables PATH, LD_LIBRARY_PATH and DYLIB_LIBRARY_PATH are defined in the command execution adding the values of the “lib” and “bin” folders of the dependencies. Allows executables to be easily run using shared libraries from its dependencies.
with_login (Optional, Defaulted to True): Pass the --login flag to bash command when using win_bash parameter. This might come handy when you don’t want to create a fresh user session for running the command.

Requiring a Conan version for the recipe

Available since: 1.28.0

A required Conan version can be declared in the conanfile.py using required_conan_version to throw an error when the Conan version installed does not meet the criteria established by the variable. To add required_conan_version to a conanfile.py just declare it before the recipe class definition:

from conans import ConanFile

required_conan_version = ">=1.27.1"

class Pkg(ConanFile):
    settings = "os", "compiler", "arch", "build_type"
    ...

It is also possible to declare required_conan_version at configuration level for the whole client adding it to the conan.conf file.