How do I check whether a file with a user-defined prefix already exists, using the while loop and if it is a case to request another prefix?


Use arcpy.Exists()

if arcpy.Exists(r"MyFeatureClass"):
    print "Feature Class Exists"
    print "Feature Class Doesn't Exist"

Additionally, look into arcpy.CreateUniqueName() to generate a new output name if the one you want to use already exists

uniqueName = arcpy.CreateUniqueName(r"MyFeatureClass")
arcpy.Buffer_analysis(r"InputFC", uniqueName, "10 Meters")

Based on what I think your code is doing, try this:

sbgfl = "sbg_fluesse" 
bufferwerte = raw_input("Enter buffer in m [split with space bar]") 
bufferwerte_2 = bufferwerte.split() 
praefix = raw_input("Enter prefix") 
for buffer_size in bufferwerte_2:
    uniqueName = arcpy.CreateUniqueName(praefix + str(buffer_size))
    arcpy.Buffer_analysis(sbgfl, uniqueName, buffer_size)

This will add a suffix number to the end of your output name to make it unique if the output name already exists.

e.g. if praefix = "roads" and buffer_size = 10, and roads10 already exists, the arcpy.CreateUniqueName() will create a output name of roads10_0 to make it unique.

And to include a notice to the user that the filename is different:

for buffer_size in bufferwerte_2:
    if arcpy.Exists(praefix + str(buffer_size)):
        print "Already exists, changing name"
    uniqueName = arcpy.CreateUniqueName(praefix + str(buffer_size))
    print "Output name = {0}".format(uniqueName)
    arcpy.Buffer_analysis(sbgfl, uniqueName, buffer_size)

Tasks such as checking for shapefiles or raster data are much more efficient using built-in Python modules. For example:


However, if you need to check for the existance of data within Esri Geodatabases, use the arcpy.Exists() command as Midavalo highlights in his answer.

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