Python code for Iterating through feature classes in a gdb to define projection

import arcpy

# Set the workspace environmentarcpy.env.workspace = r"C:\Users\abuelmc\Alignment.gdb"
# Get a list of the feature classes in the input folderfeature_classes = arcpy.ListFeatureClasses()

# Loop through the listfor fc in feature_classes:
    sr = arcpy.SpatialReference(3123)
    arcpy.DefineProjection_management(fc, sr)