Environment Variables

VTL Engine uses environment variables to configure behavior for number handling and S3 connectivity. These variables are optional and have sensible defaults.

Number Handling

These variables control how VTL Engine handles floating-point precision in comparison operators and output formatting.

Important

IEEE 754 float64 guarantees 15 significant decimal digits (DBL_DIG = 15). The valid range of 6-15 reflects the practical precision limits of double-precision floating point.

COMPARISON_ABSOLUTE_THRESHOLD

Controls the significant digits used for Number comparison operations (=, <>, >=, <=, between).

Value	Behavior
Not defined	Uses default value of 15 significant digits
6 to 15	Uses the specified number of significant digits
-1	Disables tolerance (uses Python’s default exact comparison)

The tolerance is calculated as: 0.5 * 10^(-(N-1)) where N is the number of significant digits.

For the default of 15, this gives a relative tolerance of 5e-15, which filters floating-point arithmetic artifacts while preserving meaningful differences.

OUTPUT_NUMBER_SIGNIFICANT_DIGITS

Controls the significant digits used when formatting Number values in CSV output.

Value	Behavior
Not defined	Uses default value of 15 significant digits
6 to 15	Uses the specified number of significant digits
-1	Disables formatting (uses pandas default behavior)

This variable controls the float_format parameter in pandas to_csv, using the general format specifier (e.g., %.15g) which automatically switches between fixed and exponential notation.

S3 Configuration

The following AWS environment variables are used when working with S3 URIs. This requires the vtlengine[s3] extra to be installed:

pip install vtlengine[s3]

AWS_ACCESS_KEY_ID

The access key ID for AWS authentication.

AWS_SECRET_ACCESS_KEY

The secret access key for AWS authentication.

AWS_SESSION_TOKEN

(Optional) Session token for temporary AWS credentials.

AWS_DEFAULT_REGION

(Optional) Default AWS region for S3 operations.

AWS_ENDPOINT_URL

(Optional) Custom endpoint URL for S3-compatible storage services (e.g., MinIO, LocalStack).

For more details on AWS configuration, see the boto3 documentation.

Examples

Setting comparison threshold

# Use 10 significant digits for more lenient comparisons (tolerance ~5e-10)
export COMPARISON_ABSOLUTE_THRESHOLD=10

# Use maximum precision (default, tolerance ~5e-15)
export COMPARISON_ABSOLUTE_THRESHOLD=15

# Disable tolerance-based comparison (exact floating-point comparison)
export COMPARISON_ABSOLUTE_THRESHOLD=-1

Controlling output precision

# Format output with 10 significant digits
export OUTPUT_NUMBER_SIGNIFICANT_DIGITS=10

# Disable output formatting (use pandas defaults)
export OUTPUT_NUMBER_SIGNIFICANT_DIGITS=-1

Using S3 with environment variables

# Set AWS credentials
export AWS_ACCESS_KEY_ID=your_access_key
export AWS_SECRET_ACCESS_KEY=your_secret_key
export AWS_DEFAULT_REGION=eu-west-1

from vtlengine import run

result = run(
    script="DS_r := DS_1;",
    data_structures=data_structures,
    datapoints="s3://my-bucket/input/DS_1.csv",
    output="s3://my-bucket/output/",
)

Using a custom S3 endpoint

# For S3-compatible services (MinIO, LocalStack)
export AWS_ENDPOINT_URL=http://localhost:9000
export AWS_ACCESS_KEY_ID=minioadmin
export AWS_SECRET_ACCESS_KEY=minioadmin