Attributes

name

This is a string, with a minimun of 2 and a maximum of 50 characters (though shorter names are recommended), that defines the package name. It will be the <PkgName>/version@user/channel of the package reference. It should match the following regex ^[a-zA-Z0-9_][a-zA-Z0-9_\+\.-]$, so start with alphanumeric or underscore, then alphanumeric, underscore, +, ., - characters.

The name is only necessary for export-ing the recipe into the local cache (export and create commands), if they are not defined in the command line. It might take its value from an environment variable, or even any python code that defines it (e.g. a function that reads an environment variable, or a file from disk). However, the most common and suggested approach would be to define it in plain text as a constant, or provide it as command line arguments.

version

The version attribute will define the version part of the package reference: PkgName/<version>@user/channel It is a string, and can take any value, matching the same constraints as the name attribute. In case the version follows semantic versioning in the form X.Y.Z-pre1+build2, that value might be used for requiring this package through version ranges instead of exact versions.

The version is only strictly necessary for export-ing the recipe into the local cache (export and create commands), if they are not defined in the command line. It might take its value from an environment variable, or even any python code that defines it (e.g. a function that reads an environment variable, or a file from disk). Please note that this value might be used in the recipe in other places (as in source() method to retrieve code from elsewhere), making this value not constant means that it may evaluate differently in different contexts (e.g., on different machines or for different users) leading to unrepeatable or unpredictable results. The most common and suggested approach would be to define it in plain text as a constant, or provide it as command line arguments.

description

This is an optional, but strongly recommended text field, containing the description of the package, and any information that might be useful for the consumers. The first line might be used as a short description of the package.

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"
    description = """This is a Hello World library.
                    A fully featured, portable, C++ library to say Hello World in the stdout,
                    with incredible iostreams performance"""

homepage

Use this attribute to indicate the home web page of the library being packaged. This is useful to link the recipe to further explanations of the library itself like an overview of its features, documentation, FAQ as well as other related information.

class EigenConan(ConanFile):
    name = "eigen"
    version = "3.3.4"
    homepage = "http://eigen.tuxfamily.org"

url

It is possible, even typical, if you are packaging a thid party lib, that you just develop the packaging code. Such code is also subject to change, often via collaboration, so it should be stored in a VCS like git, and probably put on GitHub or a similar service. If you do indeed maintain such a repository, please indicate it in the url attribute, so that it can be easily found.

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"
    url = "https://github.com/memsharded/hellopack.git"

The url is the url of the package repository, i.e. not necessarily the original source code. It is optional, but highly recommended, that it points to GitHub, Bitbucket or your preferred code collaboration platform. Of course, if you have the conanfile inside your library source, you can point to it, and afterwards use the url in your source() method.

This is a recommended, but not mandatory attribute.

license

This field is intended for the license of the target source code and binaries, i.e. the code that is being packaged, not the conanfile.py itself. This info is used to be displayed by the conan info command and possibly other search and report tools.

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"
    license = "MIT"

This attribute can contain several, comma separated licenses. It is a text string, so it can contain any text, including hyperlinks to license files elsewhere.

This is a recommended, but not mandatory attribute.

author

Intended to add information about the author, in case it is different from the conan user. It is possible that the conan user is the name of an organization, project, company or group, and many users have permissions over that account. In this case, the author information can explicitely define who is the creator/maintainer of the package

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"
    author = "John J. Smith (john.smith@company.com)"

This is an optional attribute

user, channel

The fields user and channel can be accessed from within a conanfile.py. Though their usage is usually not encouraged, it could be useful in different cases, e.g. to define requirements with the same user and channel than the current package, which could be achieved with something like:

from conans import ConanFile

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"

    def requirements(self):
        self.requires("Say/0.1@%s/%s" % (self.user, self.channel))

Only package recipes that are in the conan local cache (i.e. “exported”) have an user/channel assigned. For package recipes working in user space, there is no current user/channel. The properties self.user and self.channel will then look for environment variables CONAN_USERNAME and CONAN_CHANNEL respectively. If they are not defined, an error will be raised.

settings

There are several things that can potentially affect a package being created, i.e. the final package will be different (a different binary, for example), if some input is different.

Development project-wide variables, like the compiler, its version, or the OS itself. These variables have to be defined, and they cannot have a default value listed in the conanfile, as it would not make sense.

It is obvious that changing the OS produces a different binary in most cases. Changing the compiler or compiler version changes the binary too, which might have a compatible ABI or not, but the package will be different in any case.

For these reasons, the most common convention among Conan recipes is to distinguish binaries by the following four settings, which is reflected in the conanfile.py template used in the conan new command:

settings = "os", "compiler", "build_type", "arch"

When Conan generates a compiled binary for a package with a given combination of the settings above, it generates a unique ID for that binary by hashing the current values of these settings.

But what happens for example to header only libraries? The final package for such libraries is not binary and, in most cases it will be identical, unless it is automatically generating code. We can indicate that in the conanfile:

from conans import ConanFile

 class HelloConan(ConanFile):
     name = "Hello"
     version = "0.1"
     # We can just omit the settings attribute too
     settings = None

     def build(self):
         #empty too, nothing to build in header only

You can restrict existing settings and accepted values as well, by redeclaring the settings attribute:

class HelloConan(ConanFile):
    settings = {"os": ["Windows"],
        "compiler": {"Visual Studio": {"version": [11, 12]}},
        "arch": None}

In this example we have just defined that this package only works in Windows, with VS 10 and 11. Any attempt to build it in other platforms with other settings will throw an error saying so. We have also defined that the runtime (the MD and MT flags of VS) is irrelevant for us (maybe we using a universal one?). Using None as a value means, maintain the original values in order to avoid re-typing them. Then, “arch”: None is totally equivalent to “arch”: [“x86”, “x86_64”, “arm”] Check the reference or your ~/.conan/settings.yml file.

As re-defining the whole settings attribute can be tedious, it is sometimes much simpler to remove or tune specific fields in the configure() method. For example, if our package is runtime independent in VS, we can just remove that setting field:

settings = "os", "compiler", "build_type", "arch"

def configure(self):
    self.settings.compiler["Visual Studio"].remove("runtime")

options, default_options

Conan packages recipes can generate different binary packages when different settings are used, but can also customize, per-package any other configuration that will produce a different binary.

A typical option would be being shared or static for a certain library. Note that this is optional, different packages can have this option, or not (like header-only packages), and different packages can have different values for this option, as opposed to settings, which typically have the same values for all packages being installed (though this can be controlled too, defining different settings for specific packages)

Options are defined in package recipes as dictionaries of name and allowed values:

class MyPkg(ConanFile):
    ...
    options = {"shared": [True, False]}

There is an special value ANY to allow any value for a given option. The range of values for such an option will not be checked, and any value (as string) will be accepted:

class MyPkg(ConanFile):
    ...
    options = {"shared": [True, False], "commit": "ANY"}

When a package is installed, it will need all its options be defined a value. Those values can be defined in command line, profiles, but they can also (and they will be typically) defined in conan package recipes:

class MyPkg(ConanFile):
    ...
    options = {"shared": [True, False], "fPIC": [True, False]}
    default_options = "shared=False", "fPIC=False"

The options will typically affect the build() of the package in some way, for example:

class MyPkg(ConanFile):
    ...
    options = {"shared": [True, False]}
    default_options = "shared=False"

    def build(self):
        shared = "-DBUILD_SHARED_LIBS=ON" if self.options.shared else ""
        cmake = CMake(self)
        self.run("cmake . %s %s" % (cmake.command_line, shared))
        self.run("cmake --build . %s" % cmake.build_config)

Note that you have to consider the option properly in your build scripts. In this case, we are using the CMake way. So if you had explicit STATIC linkage in the CMakeLists.txt file, you have to remove it. If you are using VS, you also need to change your code to correctly import/export symbols for the dll.

This is only an example. Actually, the CMake helper already automates this, so it is enough to do:

def build(self):
    cmake = CMake(self) # internally it will check self.options.shared
    self.run("cmake . %s" % cmake.command_line) # or cmake.configure()
    self.run("cmake --build . %s" % cmake.build_config) # or cmake.build()

You can also specify default option values of the required dependencies:

class OtherPkg(ConanFile):
    requires = "Pkg/0.1@user/channel"
    default_options = "Pkg:pkg_option=value"

You can also specify default option values of the conditional required dependencies:

class OtherPkg(ConanFile):
    default_options = "Pkg:pkg_option=value"

    def requirements(self):
        if self.settings.os != "Windows":
            self.requires("Pkg/0.1@user/channel")

This will always work, on Windows the default_options for the Pkg/0.1@user/channel will be ignored, they will only be used on every other os.

If you need to dynamically set some dependency options, you could do:

class OtherPkg(ConanFile):
    requires = "Pkg/0.1@user/channel"

    def configure(self):
        self.options["Pkg"].pkg_option = "value"

Option values can be given in command line, and they will have priority over the default values in the recipe:

$ conan install -o Pkg:shared=True -o OtherPkg:option=value

You can also defined them in consumer conanfile.txt, as described in this section

[requires]
Poco/1.9.0@pocoproject/stable

[options]
Poco:shared=True
OpenSSL:shared=True

And finally, you can define options in profiles too, with the same syntax:

# file "myprofile"
# use it as $ conan install -pr=myprofile
[settings]
setting=value

[options]
MyLib:shared=True

You can inspect available package options, reading the package recipe, which is conveniently done with:

$ conan get Pkg/0.1@user/channel

requires

Specify package dependencies as a list of other packages:

class MyLibConan(ConanFile):
    requires = "Hello/1.0@user/stable", "OtherLib/2.1@otheruser/testing"

You can specify further information about the package requirements:

class MyLibConan(ConanFile):
    requires = (("Hello/0.1@user/testing"),
                ("Say/0.2@dummy/stable", "override"),
                ("Bye/2.1@coder/beta", "private"))

Requirements can be complemented by 2 different parameters:

private: a dependency can be declared as private if it is going to be fully embedded and hidden from consumers of the package. Typical examples could be a header only library which is not exposed through the public interface of the package, or the linking of a static library inside a dynamic one, in which the functionality or the objects of the linked static library are not exposed through the public interface of the dynamic library.

override: packages can define overrides of their dependencies, if they require the definition of specific versions of the upstream required libraries, but not necessarily direct dependencies. For example, a package can depend on A(v1.0), which in turn could conditionally depend on Zlib(v2), depending on whether the compression is enabled or not. Now, if you want to force the usage of Zlib(v3) you can:

class HelloConan(ConanFile):
    requires = ("A/1.0@user/stable", ("Zlib/3.0@other/beta", "override"))

This will not introduce a new dependency, it will just change Zlib v2 to v3 if A actually requires it. Otherwise Zlib will not be a dependency of your package.

version ranges

The syntax is using brackets:

class HelloConan(ConanFile):
    requires = "Pkg/[>1.0,<1.8]@user/stable"

Expressions are those defined and implemented by [python node-semver](https://pypi.org/project/node-semver/), but using a comma instead of spaces. Accepted expressions would be:

>1.1,<2.1    # In such range
2.8          # equivalent to =2.8
~=3.0        # compatible, according to semver
>1.1 || 0.8  # conditions can be OR'ed

Go to Mastering/Version Ranges if you want to learn more about version ranges.

build_requires

Build requirements are requirements that are only installed and used when the package is built from sources. If there is an existing pre-compiled binary, then the build requirements for this package will not be retrieved.

They can be specified as a comma separated tuple in the package recipe:

class MyPkg(ConanFile):
    build_requires = "ToolA/0.2@user/testing", "ToolB/0.2@user/testing"

exports

If a package recipe conanfile.py requires other external files, like other python files that it is importing (python importing), or maybe some text file with data it is reading, those files must be exported with the exports field, so they are stored together, side by side with the conanfile.py recipe.

The exports field can be one single pattern, like exports="*", or several inclusion patterns. For example, if we have some python code that we want the recipe to use in a helpers.py file, and have some text file, info.txt, we want to read and display during the recipe evaluation we would do something like:

exports = "helpers.py", "info.txt"

Exclude patterns are also possible, with the ! prefix:

exports = "*.py", "!*tmp.py"

This is an optional attribute, only to be used if the package recipe requires these other files for evaluation of the recipe.

exports_sources

There are 2 ways of getting source code to build a package. Using the source() recipe method and using the exports_sources field. With exports_sources you specify which sources are required, and they will be exported together with the conanfile.py, copying them from your folder to the local conan cache. Using exports_sources the package recipe can be self-contained, containing the source code like in a snapshot, and then not requiring downloading or retrieving the source code from other origins (git, download) with the source() method when it is necessary to build from sources.

The exports_sources field can be one single pattern, like exports_sources="*", or several inclusion patterns. For example, if we have the source code inside “include” and “src” folders, and there are other folders that are not necessary for the package recipe, we could do:

exports_sources = "include*", "src*"

Exclude patterns are also possible, with the ! prefix:

exports_sources = "include*", "src*", "!src/build/*"

This is an optional attribute, used typically when source() is not specified. The main difference with exports is that exports files are always retrieved (even if pre-compiled packages exist), while exports_sources files are only retrieved when it is necessary to build a package from sources.

generators

Generators specify which is the output of the install command in your project folder. By default, a conanbuildinfo.txt file is generated, but you can specify different generators and even use more than one.

class MyLibConan(ConanFile):
    generators = "cmake", "gcc"

Check the full generators list.

build_policy

With the build_policy attribute the package creator can change the default conan’s build behavior. The allowed build_policy values are:

missing: If no binary package is found, conan will build it without the need of invoke conan install with –build missing option.
always: The package will be built always, retrieving each time the source code executing the “source” method.

 class PocoTimerConan(ConanFile):
     build_policy = "always" # "missing"

short_paths

If one of the packages you are creating hits the limit of 260 chars path length in Windows, add short_paths=True in your conanfile.py:

from conans import ConanFile

class ConanFileTest(ConanFile):
    ...
    short_paths = True

This will automatically “link” the source and build directories of the package to the drive root, something like C:/.conan/tmpdir. All the folder layout in the conan cache is maintained.

This attribute will not have any effect in other OS, it will be discarded.

From Windows 10 (ver. 10.0.14393), it is possible to opt-in disabling the path limits. Check this link for more info. Latest python installers might offer to enable this while installing python. With this limit removed, the short_paths functionality is totally unnecessary. Please note that this only works with Python 3.6 and newer.

no_copy_source

The attribute no_copy_source tells the recipe that the source code will not be copied from the source folder to the build folder. This is mostly an optimization for packages with large source codebases, to avoid extra copies. It is mandatory that the source code must not be modified at all by the configure or build scripts, as the source code will be shared among all builds.

To be able to use it, the package recipe can access the self.source_folder attribute, which will point to the build folder when no_copy_source=False or not defined, and will point to the source folder when no_copy_source=True

When this attribute is set to True, the package() method will be called twice, one copying from the source folder and the other copying from the build folder.

folders

In the package recipe methods, some attributes pointing to the relevant folders can be defined. Not all of them will be defined always, only in those relevant methods that might use them.

self.source_folder: the folder in which the source code to be compiled lives. When a package is built in the conan local cache, by default it is the build folder, as the source code is copied from the source folder to the build folder, to ensure isolation and avoiding modifications of shared common source code among builds for different configurations. Only when no_copy_source=True this folder will actually point to the package source folder in the local cache.
self.build_folder: the folder in which the build is being done
self.install_folder: the folder in which the install has outputed the generator files, by default, and always in the local cache, is the same self.build_folder
self.package_folder: the folder to copy the final artifacts for the binary package

When executing local conan commands (for a package not in the local cache, but in user folder), those fields would be pointing to the corresponding local user folder.

cpp_info

This attribute is only defined inside package_info() method, being None elsewhere, so please use it only inside this method.

The self.cpp_info object can be filled with the needed information for the consumers of the current package:

NAME	DESCRIPTION
self.cpp_info.includedirs	Ordered list with include paths, by default [‘include’]
self.cpp_info.libdirs	Ordered list with lib paths, by default [‘lib’]
self.cpp_info.resdirs	Ordered list of resource (data) paths, by default [‘res’]
self.cpp_info.bindirs	Ordered list with include paths, by default [‘bin’]
self.cpp_info.builddirs	Ordered list with build scripts paths, by default [‘’]. CMake will search in these dirs for cmake files, like findXXX.cmake
self.cpp_info.libs	Ordered list with the library names, by default empty []
self.cpp_info.defines	Preprocessor definitions, by default empty []
self.cpp_info.cflags	Ordered list with pure C flags, by default empty []
self.cpp_info.cppflags	Ordered list with C++ flags, by default empty []
self.cpp_info.sharedlinkflags	Ordered list with linker flags (shared libs), by default empty []
self.cpp_info.exelinkflags	Ordered list with linker flags (executables), by default empty []
self.cpp_info.rootpath	Filled with the root directory of the package, see deps_cpp_info

deps_cpp_info

Contains the cpp_info object of the requirements of the recipe. In addition of the above fields, there are also properties to obtain the absolute paths:

NAME	DESCRIPTION
self.cpp_info.include_paths	Same as `includedirs` but transformed to absolute paths
self.cpp_info.lib_paths	Same as `libdirs` but transformed to absolute paths
self.cpp_info.bin_paths	Same as `bindirs` but transformed to absolute paths
self.cpp_info.build_paths	Same as `builddirs` but transformed to absolute paths
self.cpp_info.res_paths	Same as `resdirs` but transformed to absolute paths

To get a list of all the dependency names from `deps_cpp_info`, you can call the deps member:

class PocoTimerConan(ConanFile):
    ...
    def build(self):
        # deps is a list of package names: ["Poco", "zlib", "OpenSSL"]
        deps = self.deps_cpp_info.deps

It can be used to get information about the dependencies, like used compilation flags or the root folder of the package:

 class PocoTimerConan(ConanFile):
     ...
     requires = "zlib/1.2.11@conan/stable", "OpenSSL/1.0.2l@conan/stable"
     ...

     def build(self):
         # Get the directory where zlib package is installed
         self.deps_cpp_info["zlib"].rootpath

         # Get the absolute paths to zlib include directories (list)
         self.deps_cpp_info["zlib"].include_paths

         # Get the sharedlinkflags property from OpenSSL package
         self.deps_cpp_info["OpenSSL"].sharedlinkflags

env_info

This attribute is only defined inside package_info() method, being None elsewhere, so please use it only inside this method.

The self.env_info object can be filled with the environment variables to be declared in the packages reusing the recipe.

deps_env_info

You can access to the declared environment variables of the requirements of the recipe.

Note: The environment variables declared in the requirements of a recipe are automatically applied and it can be accesed with the python os.environ dictionary. Nevertheless if you want to access to the variable declared by some specific requirement you can use the self.deps_env_info object.

 import os

 class RecipeConan(ConanFile):
     ...
     requires = "package1/1.0@conan/stable", "package2/1.2@conan/stable"
     ...

     def build(self):
         # Get the SOMEVAR environment variable declared in the "package1"
         self.deps_env_info["package1"].SOMEVAR

         # Access to the environment variables globally
         os.environ["SOMEVAR"]

info

Object used to control the unique ID for a package. Check the package_id() to see the details of the self.info object.

apply_env

When True (Default), the values from self.deps_env_info (corresponding to the declared env_info in the requires and build_requires) will be automatically applied to the os.environ.

Disable it setting apply_env to False if you want to control by yourself the environment variables applied to your recipes.

You can apply manually the environment variables from the requires and build_requires:

 import os
 from conans import tools

 class RecipeConan(ConanFile):
     apply_env = False

     def build(self):
         with tools.environment_append(self.env):
             # The same if we specified apply_env = True
             pass

in_local_cache

A boolean attribute useful for conditional logic to apply in user folders local commands. It will return True if the conanfile resides in the local cache ( we are installing the package) and False if we are running the conanfile in a user folder (local Conan commands).

import os

class RecipeConan(ConanFile):
    ...

    def build(self):
        if self.in_local_cache:
            # we are installing the package
        else:
            # we are building the package in a local directory

develop

A boolean attribute useful for conditional logic. It will be True if the package is created with conan create, or if the conanfile.py is in user space:

class RecipeConan(ConanFile):

    def build(self):
        if self.develop:
            self.output.info("Develop mode")

It can be used for conditional logic in other methods too, like requirements(), package(), etc.

This recipe will output “Develop mode” if:

$ conan create user/testing
# or
$ mkdir build && cd build && conan install ..
$ conan build ..

But it will not output that when it is a transitive requirement or installed with conan install.

keep_imports

Just before the build() method is executed, if the conanfile has an imports() method, it is executed into the build folder, to copy binaries from dependencies that might be necessary for the build() method to work. After the method finishes, those copied (imported) files are removed, so they are not later unnecessarily repackaged.

This behavior can be avoided declaring the keep_imports=True attribute. This can be useful, for example to repackage artifacts

scm

Used to clone/checkout a repository. It is a dictionary with the following possible values:

from conans import ConanFile, CMake, tools

class HelloConan(ConanFile):
     scm = {
        "type": "git",
        "subfolder": "hello",
        "url": "https://github.com/memsharded/hello.git",
        "revision": "static_shared"
     }
    ...

type (Required): Currently only git supported. Others like svn will be added eventually.
url (Required): URL of the remote or auto to capture the remote from the local directory.
revision (Required):
When type is git, it can be a string with a branch name, a commit or a tag.
subfolder (Optional, Defaulted to .): A subfolder where the repository will be cloned.
username (Optional, Defauted to None): When present, it will be used as the login to authenticate with the remote.
password (Optional, Defauted to None): When present, it will be used as the password to authenticate with the remote.
verify_ssl (Optional, Defaulted to True): Verify SSL certificate of the specified url.

To know more about the usage of scm check: