generate()¶

This method will run after the computation and installation of the dependency graph. This means that it will run after a conan install command, or when a package is being built in the cache, it will be run before calling the build() method.

The purpose of generate() is to prepare the build, generating the necessary files. These files would typically be:

Files containing information to locate the dependencies, as xxxx-config.cmake CMake config scripts, or xxxx.props Visual Studio property files.
Environment activation scripts, like conanbuild.bat or conanbuild.sh, that define all the necessary environment variables necessary for the build.
Toolchain files, like conan_toolchain.cmake, that contains a mapping between the current Conan settings and options, and the build system specific syntax. CMakePresets.json for CMake users using modern versions.
General purpose build information, as a conanbuild.conf file that could contain information for some toolchains like autotools to be used in the build() method.
Specific build system files, like conanvcvars.bat, that contains the necessary Visual Studio vcvars.bat call for certain build systems like Ninja when compiling with the Microsoft compiler.

The idea is that the generate() method implements all the necessary logic, making both the user manual builds after a conan install very straightforward, and also the build() method logic simpler. The build produced by a user in their local flow should result in exactly the same one as the build done in the cache with a conan create without effort.

Generation of files happens in the generators_folder as defined by the current layout.

In many cases, the generate() method might not be necessary, and declaring the generators attribute could be enough:

from conan import ConanFile

class Pkg(ConanFile):
    generators = "CMakeDeps", "CMakeToolchain"

But the generate() method can explicitly instantiate those generators, use them conditionally (like using one build system in Windows, and another build system integration in other platforms), customize them, or provide a complete custom generation.

from conan import ConanFile
from conan.tools.cmake import CMakeToolchain

class Pkg(ConanFile):

    def generate(self):
        tc = CMakeToolchain(self)
        # customize toolchain "tc"
        tc.generate()
        # Or provide your own custom logic

The current working directory for the generate() method will be the self.generators_folder defined in the current layout.

For custom integrations, putting code in a common python_require would be a good way to avoid repetition in multiple recipes:

from conan import ConanFile
from conan.tools.cmake import CMakeToolchain

class Pkg(ConanFile):

    python_requires = "mygenerator/1.0"

    def generate(self):
        mygen = self.python_requires["mygenerator"].module.MyGenerator(self)
        # customize mygen behavior, like mygen.something= True
        mygen.generate()

In case it is necessary to collect or copy some files from the dependencies, it is also possible to do it in the generate() method, accessing self.dependencies. Listing the different include directories, lib directories from a dependency “mydep” would be possible like this:

from conan import ConanFile

class Pkg(ConanFile):

    def generate(self):
        info = self.dependencies["mydep"].cpp_info
        self.output.info("**includedirs:{}**".format(info.includedirs))
        self.output.info("**libdirs:{}**".format(info.libdirs))
        self.output.info("**libs:{}**".format(info.libs))

And copying the shared libraries in Windows and OSX to the current build folder, could be done like:

from conan import ConanFile

class Pkg(ConanFile):

    def generate(self):
        for dep in self.dependencies.values():
            copy(self, "*.dylib", dep.cpp_info.libdir, self.build_folder)
            copy(self, "*.dll", dep.cpp_info.libdir, self.build_folder)

Note

Best practices

Accessing dependencies self.dependencies["mydep"].package_folder is possible, but it will be None when the dependency “mydep” is in “editable” mode. If you plan to use editable packages, make sure to always reference the cpp_info.xxxdirs instead.

self.dependencies¶

Conan recipes provide access to their dependencies via the self.dependencies attribute. This attribute is generally used by generators like CMakeDeps or MSBuildDeps to generate the necessary files for the build.

This section documents the self.dependencies attribute, as it might be used by users both directly in recipe or indirectly to create custom build integrations and generators.

Dependencies interface¶

It is possible to access each one of the individual dependencies of the current recipe, with the following syntax:

class Pkg(ConanFile):
    requires = "openssl/0.1"

    def generate(self):
        openssl = self.dependencies["openssl"]
        # access to members
        openssl.ref.version
        openssl.ref.revision # recipe revision
        openssl.options
        openssl.settings

        if "zlib" in self.dependencies:
            # do something

Some important points:

All the information is read only. Any attempt to modify dependencies information is an error and can raise at any time, even if it doesn’t raise yet.
It is not possible either to call any methods or any attempt to reuse code from the dependencies via this mechanism.
This information does not exist in some recipe methods, only in those methods that evaluate after the full dependency graph has been computed. It will not exist in configure(), config_options, export(), export_source(), set_name(), set_version(), requirements(), build_requirements(), system_requirements(), source(), init(), layout(). Any attempt to use it in these methods can raise an error at any time.
At the moment, this information should only be used in generate() and validate() methods. For any other use, please submit a Github issue.

Not all fields of the dependency conanfile are exposed, the current fields are:

package_folder: The folder location of the dependency package binary
recipe_folder: The folder containing the conanfile.py (and other exported files) of the dependency
ref: An object that contains name, version, user, channel and revision (recipe revision)
pref: An object that contains ref, package_id and revision (package revision)
buildenv_info: Environment object with the information of the environment necessary to build
runenv_info: Environment object with the information of the environment necessary to run the app
cpp_info: includedirs, libdirs, etc for the dependency.
settings: The actual settings values of this dependency
settings_build: The actual build settings values of this dependency
options: The actual options values of this dependency
context: The context (build, host) of this dependency
conf_info: Configuration information of this dependency, intended to be applied to consumers.
dependencies: The transitive dependencies of this dependency
is_build_context: Return True if context == "build".
conan_data: The conan_data attribute of the dependency that comes from its conandata.yml file
license: The license attribute of the dependency
description: The description attribute of the dependency
homepage: The homepage attribute of the dependency
url: The url attribute of the dependency

Iterating dependencies¶

It is possible to iterate in a dict-like fashion all dependencies of a recipe. Take into account that self.dependencies contains all the current dependencies, both direct and transitive. Every upstream dependency of the current one that has some effect on it, will have an entry in this self.dependencies.

Iterating the dependencies can be done as:

requires = "zlib/1.2.11", "poco/1.9.4"

def generate(self):
    for require, dependency in self.dependencies.items():
        self.output.info("Dependency is direct={}: {}".format(require.direct, dependency.ref))

will output:

conanfile.py (hello/0.1): Dependency is direct=True: zlib/1.2.11
conanfile.py (hello/0.1): Dependency is direct=True: poco/1.9.4
conanfile.py (hello/0.1): Dependency is direct=False: pcre/8.44
conanfile.py (hello/0.1): Dependency is direct=False: expat/2.4.1
conanfile.py (hello/0.1): Dependency is direct=False: sqlite3/3.35.5
conanfile.py (hello/0.1): Dependency is direct=False: openssl/1.1.1k
conanfile.py (hello/0.1): Dependency is direct=False: bzip2/1.0.8

Where the require dictionary key is a “requirement”, and can contain specifiers of the relation between the current recipe and the dependency. At the moment they can be:

require.direct: boolean, True if it is direct dependency or False if it is a transitive one.
require.build: boolean, True if it is a build_require in the build context, as cmake.
require.test: boolean, True if its a build_require in the host context (defined with self.test_requires()), as gtest.

The dependency dictionary value is the read-only object described above that access the dependency attributes.

The self.dependencies contains some helpers to filter based on some criteria:

self.dependencies.host: Will filter out requires with build=True, leaving regular dependencies like zlib or poco.
self.dependencies.direct_host: Will filter out requires with build=True or direct=False
self.dependencies.build: Will filter out requires with build=False, leaving only tool_requires in the build context, as cmake.
self.dependencies.direct_build: Will filter out requires with build=False or direct=False
self.dependencies.test: Will filter out requires with build=True or with test=False, leaving only test requirements as gtest in the host context.

They can be used in the same way:

requires = "zlib/1.2.11", "poco/1.9.4"

def generate(self):
    cmake = self.dependencies.direct_build["cmake"]
    for require, dependency in self.dependencies.build.items():
        # do something, only build deps here

Dependencies `cpp_info` interface¶

The cpp_info interface is heavily used by build systems to access the data. This object defines global and per-component attributes to access information like the include folders:

def generate(self):
    cpp_info = self.dependencies["mydep"].cpp_info
    cpp_info.includedirs
    cpp_info.libdirs

    cpp_info.components["mycomp"].includedirs
    cpp_info.components["mycomp"].libdirs

All the paths declared in the cppinfo object (like cpp_info.includedirs) are absolute paths and works whether the dependency is in the cache or is an editable package.