diff --git a/catalog_tools/catalog.py b/catalog_tools/catalog.py
index 4257039..2e5ebf7 100644
--- a/catalog_tools/catalog.py
+++ b/catalog_tools/catalog.py
@@ -1,3 +1,5 @@
+import functools
+
 import pandas as pd
 from geopandas import GeoDataFrame
 
@@ -5,7 +7,7 @@
                  'time', 'magnitude', 'magnitude_type']
 
 
-def _check_required_cols(df):
+def _check_required_cols(df, required_cols=REQUIRED_COLS):
     if not set(REQUIRED_COLS).issubset(set(df.columns)):
         return False
     return True
@@ -18,6 +20,30 @@ def _catalog_constructor_with_fallback(*args, **kwargs):
     return df
 
 
+def require_cols(_func=None, *,
+                 require: list[str] = REQUIRED_COLS,
+                 exclude: list[str] = None):
+    def decorator_require(func):
+        @functools.wraps(func)
+        def wrapper_require(self, *args, **kwargs):
+            nonlocal require
+            if exclude:
+                require = [col for col in require if col not in exclude]
+            if not _check_required_cols(self, require):
+                raise AttributeError(
+                    'Catalog is missing the following columns '
+                    f'for execution of the method "{func.__name__}": '
+                    f'{set(require).difference(set(self.columns))}.')
+            value = func(self, *args, **kwargs)
+            return value
+        return wrapper_require
+
+    if _func is None:
+        return decorator_require
+    else:
+        return decorator_require(_func)
+
+
 class Catalog(pd.DataFrame):
 
     _metadata = ['name']
@@ -31,24 +57,46 @@ def __init__(self, data=None, *args, name=None, **kwargs):
     def _constructor(self):
         return _catalog_constructor_with_fallback
 
+    @require_cols
+    def get_magnitude(self):
+        return self['magnitude'].values
+
 
 def main():
-    # df = Catalog([{'a': 3, 'b': 2, 'c': 3}], name='cat')
+    df_no = Catalog([{'a': 3, 'b': 2, 'c': 3}], name='cat')
+
+    df_yes = Catalog([{'longitude': 1, 'latitude': 2, 'depth': 3,
+                       'time': 4, 'magnitude': 5, 'magnitude_type': 6,
+                       'magnitude_Mw': 7}], name='cat')
+
+    print(type(df_yes))
 
-    # # df['a'] = [1, 2, 3]
-    # # df['b'] = [4, 5, 6]
-    # # df['c'] = [7, 8, 9]
+    # df['a'] = [1, 2, 3]
+    # df['b'] = [4, 5, 6]
+    df_no['d'] = [7]
 
+    print(df_no.get_magnitude())
+    # print(df_yes)
     # df2 = df[['a', 'b']]
     # print(type(df))
     # print(df)
     # print(type(df2))
     # print(df2)
 
-    gdf = GeoDataFrame()
-    gdf = gdf.from_dict([{'a': 3, 'b': 2, 'c': 3}])
-    print(gdf.area)
-    print(type(gdf[['a', 'b']]))
+    # gdf = GeoDataFrame()
+    # print(type(gdf))
+    # gdf = gdf.from_dict([{'a': 3, 'b': 2, 'c': 3}])
+    # print(gdf.area)
+    # print(type(gdf))
+    # print(type(gdf[['a', 'b']]))
+
+    # url = 'https://earthquake.usgs.gov/fdsnws/event/1/query'
+    # url = 'http://arclink.ethz.ch/fdsnws/event/1/query'
+    # client = FDSNWSEventClient(url)
+    # cat = client.get_events(
+    #     start_time=datetime(2010, 7, 1),
+    #     end_time=datetime(2020, 7, 1),
+    #     include_all_magnitudes=False)
 
 
 if __name__ == '__main__':