diff --git a/doc/conf.py b/doc/conf.py
index 691a432619d5acd255324a30e337f7c4d6305f59..782acf1a7f8bfe4d20b40195a07d40da623ca294 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -21,11 +21,11 @@ from pkg_resources import get_distribution
 
 # -- Project information -----------------------------------------------------
 
-version = get_distribution('km3irf').version
-short_version = '.'.join(version.split('.')[:2])
-project = 'km3irf {}'.format(short_version)
-copyright = '{0}, Tamas Gal'.format(date.today().year)
-author = 'Tamas Gal'
+version = get_distribution("km3irf").version
+short_version = ".".join(version.split(".")[:2])
+project = "km3irf {}".format(short_version)
+copyright = "{0}, Tamas Gal".format(date.today().year)
+author = "Tamas Gal"
 
 # -- General configuration ---------------------------------------------------
 
@@ -33,32 +33,34 @@ author = 'Tamas Gal'
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
-    'sphinx.ext.autodoc', 'sphinx.ext.autosummary', 'sphinx.ext.viewcode',
-    'autoapi.extension', 'numpydoc',
-    'sphinx_gallery.gen_gallery'
+    "sphinx.ext.autodoc",
+    "sphinx.ext.autosummary",
+    "sphinx.ext.viewcode",
+    "autoapi.extension",
+    "numpydoc",
+    "sphinx_gallery.gen_gallery",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
-templates_path = ['_templates']
+templates_path = ["_templates"]
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.
-exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', 'version.py']
+exclude_patterns = ["_build", "Thumbs.db", ".DS_Store", "version.py"]
 
 # AutoAPI
 autoapi_type = "python"
-autoapi_dirs = ['../src/km3irf']
+autoapi_dirs = ["../src/km3irf"]
 autoapi_options = ["members", "undoc-members", "show-module-summary"]
 autoapi_include_summaries = True
 
 # Gallery
 sphinx_gallery_conf = {
-    'backreferences_dir': 'gen_modules',
-    'default_thumb_file': '_static/default_gallery_thumbnail.png',
-    'examples_dirs': '../examples',  # path to your example scripts
-    'gallery_dirs':
-    'auto_examples',  # path to where to save gallery generated output
+    "backreferences_dir": "gen_modules",
+    "default_thumb_file": "_static/default_gallery_thumbnail.png",
+    "examples_dirs": "../examples",  # path to your example scripts
+    "gallery_dirs": "auto_examples",  # path to where to save gallery generated output
 }
 
 # -- Options for HTML output -------------------------------------------------
@@ -66,11 +68,11 @@ sphinx_gallery_conf = {
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'sphinx_rtd_theme'
+html_theme = "sphinx_rtd_theme"
 html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ["_static"]
 html_title = "km3irf {}".format(version)
diff --git a/src/km3irf/__init__.py b/src/km3irf/__init__.py
index ab1f2f1a3c4f9d51e0a02c0d7b388ac5ecee6fc0..bcb15951a0adbf12dc69d9944830cb2d52b54697 100644
--- a/src/km3irf/__init__.py
+++ b/src/km3irf/__init__.py
@@ -3,4 +3,5 @@ from pkg_resources import get_distribution, DistributionNotFound
 version = get_distribution(__name__).version
 
 from .calc import Calculator
-# from .data import list_data
\ No newline at end of file
+
+# from .data import list_data
diff --git a/src/km3irf/utils.py b/src/km3irf/utils.py
index 85bdeda8a018755747cd05d78aef4d00c8ae7cae..4279cea8063dae3a7e69ddf5850e667e9b8b3f0f 100644
--- a/src/km3irf/utils.py
+++ b/src/km3irf/utils.py
@@ -1,13 +1,15 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
+from cmath import inf
 from .calc import Calculator
 from astropy.io import fits
-from os import path
+from os import path, listdir
 from glob import glob
 from os.path import getsize
 from prettytable import PrettyTable
 from importlib_resources import files
-data_dir = path.join(path.dirname(__file__), 'data')
+
+data_dir = path.join(path.dirname(__file__), "data")
 
 
 def print_multiplication_table(base):
@@ -17,31 +19,41 @@ def print_multiplication_table(base):
         print("{} x {} = {}".format(base, i, calculator.multiply(base, i)))
 
 
-def merge_fits(aeff_fits=path.join(data_dir, "aeff.fits"), 
-               psf_fits=path.join(data_dir, "psf.fits"), 
-               edisp_fits=path.join(data_dir, "edisp.fits"),
-               bkg_fits=path.join(data_dir, "bkg_nu.fits"),
-               output_file='all_in_one.fits'):
-    """Merge separated fits files into one, which can be used in gammapy"""
+def merge_fits(
+    aeff_fits=path.join(data_dir, "aeff.fits"),
+    psf_fits=path.join(data_dir, "psf.fits"),
+    edisp_fits=path.join(data_dir, "edisp.fits"),
+    bkg_fits=path.join(data_dir, "bkg_nu.fits"),
+    output_file="all_in_one.fits",
+):
+    """
+    Merge separated fits files into one, which can be used in gammapy
+
+    aeff_fits: path to Aeff .fits file
+    psf_fits: path  to PSF .fits file
+    edisp_fits: path to Edisp .fits file
+    bkg_fits: path to Background .fits file
+    output_file: name of the merged .fits file in data foledr of the package
+    """
     hdu_list = []
     hdu_list.append(fits.PrimaryHDU())
 
-    file_aeff = fits.open(aeff_fits) 
+    file_aeff = fits.open(aeff_fits)
     hdu_list.append(file_aeff[1])
-    hdu_list[1].name = 'EFFECTIVE AREA'
+    hdu_list[1].name = "EFFECTIVE AREA"
 
     file_psf = fits.open(psf_fits)
     hdu_list.append(file_psf[1])
-    hdu_list[2].name = 'POINT SPREAD FUNCTION'
+    hdu_list[2].name = "POINT SPREAD FUNCTION"
 
     file_edisp = fits.open(edisp_fits)
     hdu_list.append(file_edisp[1])
-    hdu_list[3].name = 'ENERGY DISPERSION'
+    hdu_list[3].name = "ENERGY DISPERSION"
 
     file_bkg = fits.open(bkg_fits)
     hdu_list.append(file_bkg[1])
-    hdu_list[4].name = 'BACKGROUND'
-    
+    hdu_list[4].name = "BACKGROUND"
+
     new_fits_file = fits.HDUList(hdu_list)
     new_fits_file.writeto(path.join(data_dir, output_file), overwrite=True)
 
@@ -50,16 +62,23 @@ def merge_fits(aeff_fits=path.join(data_dir, "aeff.fits"),
     file_edisp.close()
     file_bkg.close()
 
-def list_data():
-    """Prints the table with content of data folder"""
-    tab = PrettyTable(["File Path","Size, KB"], align="l")
-    # data_path = path.join(f"{files('km3irf')}","data","*.fits")
-    data_path = path.join(data_dir,"*.fits")
-    # for file in glob(f"{files('km3irf')}/data/*.fits", recursive=True):
-    for file in glob(data_path, recursive=True):
-        #add row with file name and size in KB
-        tab.add_row([file, round(getsize(filename=file)/float(1<<10), 2)])
 
-    print(tab)
+def list_data(print_tab=False):
+    """
+    Return dictionary with names and pathes in the data folder
+
+    print_tab: print a table with content, default False
+    """
+    tab = PrettyTable(["File Path", "Size, KB"], align="l")
+    data_path = path.join(data_dir, "*.fits")
+    info = {}
+
+    for file, i in zip(glob(data_path, recursive=True), listdir(data_dir)):
+        tab.add_row([file, round(getsize(filename=file) / float(1 << 10), 2)])
+        info.update({i: file})
+
+    if print_tab:    
+        print(tab)
+    
+    return info
 
-# merge_fits()
\ No newline at end of file
diff --git a/tests/test_is_mandatory.py b/tests/test_is_mandatory.py
index d0ff27466e13ac33b00af975f5f7a2bdfdff9ab2..25695ab0ff60d93ccdaba79606d70be64c475aa7 100644
--- a/tests/test_is_mandatory.py
+++ b/tests/test_is_mandatory.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
 
+
 def test_is_mandatory():
     assert 2 == 5 - 3