SciPy - readsav() Function

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The scipy.io.readsav() method reads and interprets the .sav files from the Interactive Data Language, IDL. These files are structured scientific data in arrays and records. This function helps users transition from IDL to Python or work with both languages.

This method becomes very helpful to scientists and researchers whenever they require to handle the old data in the .sav format. This method introduces IDL-generated data into the workflows of Python that makes users perform complicated analysis, visualize, and manipulate data in the vast environment of Python.

Errors can occur while using readsav() method, if the file .sav has an unsupported file format, or even incomplete data, or wrong structure. Other issues may arise, such as a misunderstanding of the data structure where nested records or unsuitable compression methods could cause runtime errors or incomplete data retrieval.

The uncompressed_file_name parameter is very helpful when you are working with compressed .sav files. It allows you to select a temporary location for the compressed data. The verbose parameter is useful for debugging. It prints out lots of detail about files, which can be helpful in finding errors in variables or how files are configured.

Syntax

The syntax for the SciPy readsav() method is as follows −

.readsav(file_name, idict=None, python_dict=False, uncompressed_file_name=None, verbose=False)

Parameters

This method accepts the following parameters −

• file_name − The name of the .sav file to read.

• idict − If provided, the contents of the .sav file will be stored in this dictionary instead of creating a new dictionary.

• python_dict − If True, the function returns a Python dictionary. If False, it returns a scipy.io.idl.AttrDict object, which provides attribute-style access to variables in the .sav file.

• uncompressed_file_name − If the .sav file is compressed, this parameter specifies the name of a temporary file where the uncompressed data will be stored.

• verbose − If True, the function prints information about the contents of the file being read.

Return Value

AttrDict or dict − The object containing the data from the .sav file. The type depends on the value of python_dict.

Example 1

This is a basic example of using the readsav() function to load a .sav file and print its keys. The keys represent the variables stored in the file, helping us understand its structure.

from scipy.io import readsav

# Load the .sav file
data = readsav('example.sav')

# Print keys of the .sav file
print("Keys in the .sav file:")
print(data.keys())

Example 2

This example uses readsav() method to access and print a specific variable from a .sav file using its key.

from scipy.io import readsav

# Load the .sav file
data = readsav('example.sav')

# Access and print a specific variable
print("Content of 'variable_name':")
print(data['variable_name'])  # Replace 'variable_name' with the actual key

Example 3

The readsav() method throws an Invalid SIGNATURE error when used on unsupported formats like .mat files.

Let us create a .mat file with a variable and try reading it using readsav(), which raises an error: Invalid SIGNATURE: b'MA' because .mat files are not valid for readsav.

import scipy.io
from scipy.io import readsav

# Create a `.mat` file
scipy.io.savemat('example.mat', {'example_variable': [1, 2, 3]})

# Try reading the `.mat` file with `readsav` (this will raise an error)
try:
    data = readsav('example.mat')
    print("Keys in the .sav file:")
    print(data.keys())
except Exception as e:
    print("Error:", e)

Output of the above code is as follows −

Error: Invalid SIGNATURE: b'MA'

Example 4

Corrupted .sav files cause an Invalid SIGNATURE error because the file structure is invalid.

In the below code we create a invalid .sav file with invalid binary content and try reading it. This results in Error: Invalid SIGNATURE: b'IN', showing readsav() only supports valid .sav files.

# Create a invalid .sav file with invalid content
with open('corrupted.sav', 'wb') as f:
    f.write(b'INVALID_CONTENT')

# Try reading the corrupted file
try:
    data = readsav('corrupted.sav')
    print("Keys in the .sav file:")
    print(data.keys())
except Exception as e:
    print("Error:", e)

Following is an output of the above code −

Error: Invalid SIGNATURE: b'IN'

Example 5

If a .sav file is missing, readsav() raises a FileNotFoundError.

In the below code, We attempted to read a non-existent file named nonexistent.sav, which raised Error: [Errno 2] No such file or directory.

from scipy.io import readsav

# Try reading a non-existent file
try:
    data = readsav('nonexistent.sav')
except FileNotFoundError as e:
    print("Error:", e)

Following is an output of the above code −

Error: [Errno 2] No such file or directory: 'nonexistent.sav'