Flags are user-specified inputs to an operation. Flags can define any type of information. Flags are commonly used for:

  • Hyperparameters
  • Data file locations
  • Data set names
  • Other operation confirmation

Flags are specified for an operation using NAME=VALUE arguments to guild run.

The following command sets two flag values:

guild run train learning-rate=0.1 batch-size=100

Flags values can also be provided in batch files.

Flags Interface

Guild makes flag values available to a script using a flags interface. Guild supports different interfaces:

  • Command line arguments
  • Environment variables
  • Python global variables

Guild works across platforms and languages using standard interfaces when possible. Guild does not require changes to script code to support Guild-specific configuration. Guild uses script inspection and explicit configuration in Guild files for flag information.

When Guild does not have explicit configuration (e.g. when a script is run directly) it attempts to infer the flags interface by inspecting the script. See Default Behavior for more information.

The flags interface is configured for an operation using the flags-dest attribute. See flags-dest in Guild File Reference for configuration details.

For example of different interfaces, see Guild File Cheatsheet.

Command Line Arguments

Unless otherwise configured (or inferred by inspecting the script), Guild uses a command line interface to pass flag values to a script.

This interface can be explicitly configured by setting flags-dest to args.

Flag values are included as command line arguments using the format:


By default, FLAG_ARG_NAME is the flag name. If the arg-name attribute is specified for a flag definition, Guild uses the attribute value instead.

ENCODED_FLAG_VALUE is the string-encoded flag value.

Each non-null flag value is specified as arguments following this format.

Consider the following command:

guild run train.py learning-rate=0.1 batch-size=100

Guild passes the two flag values to train.py as follows:

python -m train --learning-rate 0.1 --batch-size 100

The following Guild file configuration changes the argument names for each flag:

      arg-name: lr
      arg-name: bs

In this case, Guild passes the two flag values as:

python -m train --lr 0.1 --bs 100

Tip Use the --print-cmd option with guild run to print the full command Guild uses when running an operation.

Environment Variables

Guild makes flag values available as environment variables to each run process. Environment variables are named FLAG_UPPER_CASE_NAME. UPPER_CASE_NAME is the flag name coverted to upper case with non-alphanumeric characters converted to undercore characters.

For example, the value for flag x is read as the environment variable FLAG_X.

Use the env-name flag attribute to specify a different environment variable name for a flag.

For example, the following configuration causes Guild to set values of x using the environment variable X instead of FLAG_X:

      env-name: X

Tip Use environment variables as a convenient way to read flag values without having to process command line arguments.

Python Global Variables

Guild sets flag values as global variables in a Python script when flags-dest is set to globals or when Guild otherwise detects this interface through inspection.

Guild only sets global variables when they are already defined in a script. Guild does not create new variables in a script.

The following operation uses a global variables interface to set values for flags x and y:

  flags-dest: globals
  flags-import: [x, y]

Here is a Python script that uses x and y:

x = 1
y = 2

print("z: %i" % (x + y))

You can alternatively set flag values in a Python global dict variable using global:VARIABLE_NAME for flags-dest.

The following configuration sets flag values as items in the params global variable.

  flags-dest: global:params
  flags-import: [x, y]

The following Python script shows how train might be implemented using params:

params = {"x": 1, "y": 2}

print("z: %i" % (params["x"] + params["y"]))

Import Flags

To avoid duplicating flag definitions in scripts and in Guild files, Guild lets you import flag definitions.

Flag Detection

To import flags, Guild inspects a script and look for possible flag definitions based on the flags interface. As described above, the flags interface can be explicitly configured. Otherwise Guild attempts to infer the interface.

Guild uses the rules below for inferring flags according to the specified interface.

Interface Detection Method
args Guild runs the script with the --help option and inspects argparse generated option. From this Guild infers flag name, description, type, available choices, and default value.
globals Guild inspects the Python module and looks for global variables that are assigned numbers, strings, or boolean constants. Guild does not import variables that start with _. From this Guild infers flag name, type, and default value.
global:<name> Guild inspects the Python module and looks for the specified global variable. Guild infers flags if the variable references a dict. Guild infers flags from dict items that are number, string, or boolean constants. From these items, Guild infers flag name, type, and default value.

Guild does not currently support flag imports for non-Python scripts. In such cases, explicitly define each flag and use command line arguments or environment variables (see above) to access flags.

Flag Import Configuration

Guild supports different import scenarios:

  • Import all detected flags
  • Import a list of detected flags
  • Import all but some detected flags
  • Explicitly disable flag imports
Import All Flags

To import all detected flags, use the value all or yes for flags-import.

  flags-import: all
Import Some Flags

To import a list of detected flags, specify the flag names in a list.

  flags-import: [x, y, z]
Import All but Some Flags

You can combine flags-import: all with flags-import-skip to import all flags but skip those specified.

  flags-import: all
  flags-import-skip: [x, y]

This pattern is useful when Guild mistakenly infers a command line option or variable as a flag.

Explicitly Disable Flags Import

To disable Guild support for detecting and importing flags, use the value no for flags-import.

  flags-import: no

In this case, you must explicitly define each flag your script supports.

Tip When flags-import is no, Guild does not inspect your script for flags. Use this value to avoid processing your scripts when you don’t need to.

Flag Definitions

Define flags for an operation using the flags operation attribute.

    learning-rate: 0.01
    batch-size: 100

Each flag is defined by a key in the flags mapping. The key is the flag name.

Flags can be defined using a value, as shown above, or with a mapping of attributes. If a value is specified, it’s used as the default flag value. The default value can otherwise be defined using the default attribute. The following is equivalent to the configuration above:

      default: 0.01
      default: 100

Flags support a number of attributes for defining settings for help, value checks, type conversion, and interface details. Refer to Guild File Reference for a list of supported attributes.

For more examples of flag definitions, see Guild File Cheatsheet.

Batch Files

Batch files are files that contain one or more sets of flags to use for a run.

Specify batch files for a run using one or more arguments with the syntax @PATH where PATH is the path to a valid batch file.

For example, to use the batch file trials.csv for operation train, run:

guild run @trials.csv

For information on batch file format, see Batch Files.

Special Flag Values

Guild supports a number of special flag value types that influence the way Guild runs an operation.

Value List Used in manual searches to generate runs for a list of values.
Sequence Function Used in grid search to generate a sequential list of values.
Search Space Function Used in random search and other optimizers to specify a search space.

Value Lists

A value list is a flag value in the format [VAL1,VAL2,] where each value is a number, a string, or boolean value.

A value list is processed according to the batch operation used. The default batch operation uses values in a grid search. Other batch operations, including random and sequetial optimizers, use the list as a set of choices to select from when suggesting trial values.

The following command is a grid search. It runs the train operation a total of nine times — one for each combination of values defined by value lists:

guild run train lr=[0.001,0.01,0.1] batch-size=[100,500,1000]

This command is a sequential optimization using gp to minimize loss. It uses the same flag values. Based on the optimizer, it generates 5 trials using value lists as choices to sample from:

guild run train lr=[0.001,0.01,0.1] batch-size=[100,500,1000] -o gp -m 5

Sequence Functions

Sequence functions are specified in the format NAME[ARGS] where NAME is one of the functions below and ARGS is a list of values separated by a colon :.

Function Name Description
range Range with start, end, and an optional step size
linspace Evenly spaced sequence along a linear scale with start, end, and an optional value count
logspace Evenly spaced sequence along a log-linear scale with start, end, an optional value count, and an optional logarithmic base



Generates a list of values starting with START and ending with END in increments of STEP. STEP can be omitted, in which case the value 1 is used.

Example Sequence
range[1:4] [1, 2, 3, 4]
range[1:4:2] [1, 3]
range[0:0.3:0.1] [0.0, 0.1, 0.2, 0.3]



Generates COUNT values that are evenly spaced between START and END inclusively.

Example Sequence
linspace[1:5] [1.0, 2.0, 3.0, 4.0, 5.0]
linspace[1:5:3] [1.0, 3.0, 5.0]



Generates COUNT values along a logarithmic scale between BASE ^ LOW and BASE ^ HIGH inclusively.

Example Sequence
logspace[1:5] [10.0, 100.0, 1000.0, 10000.0, 100000.0]
logspace[0:4:3] [1.0, 100.0, 10000.0]
logspace[-4:-1:4] [0.0001, 0.001, 0.01, 0.1]
logspace[0:2:3:2] [1.0, 2.0, 4.0]

Search Space Functions

Search space functions are specified in the format NAME[ARGS] where NAME is one of the functions below and ARGS is a list of values separated by a colon :.

Function Name Description
uniform Uniform distribution over a range of values
loguniform Log-uniform distribution over a range of values



Alternative syntax (omits function name):


Search space from START to END from a uniform distribution.



Search space from START to END from a log-uniform distribution.

Flag Value Decoding

Guild uses the YAML spec for decoding strings to values.


String Value Decoded Type
hello string
1 int
1.0 float
1e2 float
'1e2' string
[1,2,3] list

Guild provides an exception in cases where a string that appears to be a run ID but would otherwise be treated by YAML as scientific notation.

String Value Decoded Type
1e10 string
67217e15 string

In cases where a flag must interpret these values as floats, specify the type attribute as float for the flag definition.

For example:

      type: float

In this case, Guild will explicitly decode string input to float.