topic Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e in Python Questions

ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation err

ScottChang — Sun, 12 Dec 2021 01:22:54 GMT

Hi all
I am using the following tutorial materials to pick up the Python programming:

(i) Python Programming for ArcGIS by David Quinn & Daniel Sheehan (dated: January 27, 2011)

(ii) Python �?? Check for number of shapefiles in a directory in http://gis.stackexchange.com/questions/30059

I tried the following ArcPy code in my ArcMap 10:

 >>> import arcpy
>>> import os
>>> import glob 
>>> # Check numbers of shapefiles in a directory
>>> path = "C:\\TEMP\\"
>>> first = glob.glob(os.path.join(path,"NavyAnnexPt06move*"))
>>> first 
['C:\\TEMP\\NavyAnnexPt06move.dbf', 'C:\\TEMP\\NavyAnnexPt06move.prj', 'C:\\TEMP\\NavyAnnexPt06move.sbn', 'C:\\TEMP\\NavyAnnexPt06move.sbx', 'C:\\TEMP\\NavyAnnexPt06move.shp', 'C:\\TEMP\\NavyAnnexPt06move.shx']
>>> # Also to check for the only filename in path
 
>>> def file_check(path):
...      """Returns true if in path there is only one basename"""
... import os
... mlist = []I am using the following tutorial materials to pick up the Python programming:
...       for file in os.listdir(path):
...           if os.path.basename(file).split(".")[0] not in mlist:
...              mlist.append(os.path.basename(file).split(".")[0])
...     if len(mlist)>1:
...              return True
...       else:
...              return False
... 

Parsing error <type 'exceptions.IndentationError'>: unexpected indent (line 5)
>>>

and I got an indentation error. Please help, advise and respond.

Thanks,
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

curtvprice — Sun, 12 Dec 2021 01:22:57 GMT

I got an indentation error. Please help, advise and respond.

You must be fanatically consistent with indents. Do not mix tabs and spaces and make sure your indents are absolutely aligned for each block of code.

If you're not using an IDE (IDLE, PythonWin, PyScripter, WingIDE are the big four) I highly recommend it!

Here's an example of your function properly indented:

"""Returns true if in path there is only one basename"""
import os
mlist = [] 
for file in os.listdir(path):
    if os.path.basename(file).split(".")[0] not in mlist:
        mlist.append(os.path.basename(file).split(".")[0])
    if len(mlist)>1:
            return True
        else:
            return False

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Tue, 21 Aug 2012 18:11:07 GMT

Hi Curtis, Thanks for your nice response.

I tried to do the "block alignment" things you instructed. But, I still failed to get it right-see the attached file for details.
Please kindly help, advise and respond again.

Thanks,
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

curtvprice — Sun, 12 Dec 2021 01:22:59 GMT

Scott, here's what you sent:

[ATTACH=CONFIG]17142[/ATTACH]

The error is the entire function's contents need to be indented. The docstring is not a comment, it's actual code, so it must be indented too.

def function():
    """This is my function""" 
    print "Hello world"
    return

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Wed, 22 Aug 2012 11:23:33 GMT

Hi Curtis, Thanks for your response.

I tried my best to do the whole "block alignment" identation - see the attached file. I executed it and I got: Parsing error <type 'exceptions.IndentationError'>: unindent does not match any outer indentation level (line 10). I am completely lost now. Please help, advise and respond again.

Thanks,
Scott Chang

P. S. I also tried your "def function(): ......." No "Hello world" is printed out in the Python Window of my ArcGIS 10 Desktop program!!?? Any comments on this thing I tried?

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

curtvprice — Wed, 22 Aug 2012 15:23:37 GMT

Parsing error <type 'exceptions.IndentationError'>: unindent does not match any outer indentation level (line 10).

Your indentation syntax online 10. The "else" statement must be at the same indent level as "if". (see" rel="nofollow" target="_blank">http://docs.python.org/tutorial/controlflow.html](see the Python help) (This was my error - I moved your else in the wrong direction when I was fixing your code.)

I highly recommend going through the Python" rel="nofollow" target="_blank">http://docs.python.org/tutorial/index.html]Python tutorial, it gets you up to speed on things like this fast.

I also tried your "def function(): ......." No "Hello world" is printed out in the Python Window of my ArcGIS 10 Desktop program!!?? Any comments on this thing I tried?

You need to use arcpy.AddMessage to send messages from script tools. Print only works in your IDE, command line, or an interactive python prompt (">>>") (btw a great place to test code).

Arc 10.1 help: Writing" rel="nofollow" target="_blank">http://resources.arcgis.com/en/help/main/10.1/index.html#//00150000000p000000]Writing messages in script tools

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Sun, 12 Dec 2021 01:23:02 GMT

Hi Curtis, Thanks for your nice response.
In the last several days, I went through the first 9 chapters of the Python tutorial, and the basic stuff of 2 Python books ("Python Programming for the absolute beginner" [3rd Edition] by Michael Dawson and "The Quick Python Book" by Vernon L. Ceder) to pick up the essential, basic skills of Python programming. This morning, I executed the following ArcPy script in the ArcMap 10.0 of my "IAP2011-Quinn.mxd" project:

 >>> import arcpy
>>> import os
>>> import glob 
>>> path = "C:\\TEMP\\"
>>> def file_check(path):
...     """Returns true if path there is only one basename"""
...     import os
...     mlist = []
...     for file in os.listdir(path):
...         if os.path.basename(file).split(".") not in mlist:
...             mlist.append(os.path.basename(file).split(".")[0])
...         if len(mlist)>1:
...             return True
...         else:
...             return False
... 
>>>

I executed this set of the ArcPy code statements. It ran OK without any error message. But it did not give me the output. I do not what it is happening in executing this ArcPy script. Please kindly help, advise and respond again.

Many Thanks again.
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

curtvprice — Sun, 12 Dec 2021 01:23:05 GMT

Looking good. Can't overstate the usefulness of that Python tutorial!

Your function looks fine - but you need to run it:

>>> file_check(path)

One little thing, there is another os function that will avoid a bug in your program if there are extra dots in your file name.

instead of using split(), os.path.splitext():

for file in os.listdir(path):
    basename = os.path.splitext(os.path.basename(file))[0]
    if basename not in mlist:
        mlist.append(basename)

Also - your last if statement is inside the loop, I think you want it to dedent so it will run after the for loop is done.

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Sun, 12 Dec 2021 01:23:08 GMT

Hi Curtis, Thanks for your nice, valuable response.
(1) I got the "False" ouput from my old arcpy script and your new arcpy script.
(2) I copied a new arcpy script for class Circle from Page 187 of Vernon L. Ceder's "The Quick Python Book". I executed the arcpy script in my ArcGIS 10.0 and I got a Runtime error <type 'exceptions.AttributeError'>....:

 >>> import arcpy
>>> import os
>>> import glob 
>>> path = "C:\\TEMP\\"
>>> def file_check(path):
...     """Return true if path there is only one basename"""
...     import os
...     mlist = []
...     for file in os.listdir(path):
...         basename = os.path.splitext(os.path.basename(file))[0]
...         if basename not in mlist:
...             mlist.append(basename)
...         if len(mlist)>1:
...             return True
...         else:
...             return False
...    
... 
>>> file_check(path)
False
>>> class Circle:
...     def _init_(self):
...         self.radius = 1
... my_circle = Circle()
... print (2 * 3.14 * my_circle.radius)
... my_circle.radius = 5
... print (2 * 3.14 * my_circle.radius)
... 
Runtime error <type 'exceptions.AttributeError'>: Circle instance has no attribute 'radius'

This is new to me and I have no ideas what is wrong in my arcpy script that was executed in my ArcGIS 10.0. Please kindly help and advise.

Thanks again,
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ThomasEmge — Sun, 12 Dec 2021 01:23:10 GMT

Scott,

the answer is in the Python documentation at http://docs.python.org/tutorial/classes.html

As Curtis suggested I would also recommend that you take your time working through the tutorial. Python is not a "hard" language to learn but it is still a matter of getting the concept right and understanding what the code is doing. If you are not already fluent in other coding languages it simply means that the learning process will take time. Depending on your prior coding experience it might mean that it will take a couple of weeks before you can generate code of the fly.

For classes there special methods invoked throughout the lifetime of an object (an instance of a class). The method called at the creation of the object is called __init__(self[,...]). Notice the double underscores. The arguments are a reference to itself and optionally a list of arguments

class Circle:
    def __init__(self):
        self.radius = 1

which means that at the time of Circle object creation you are adding an attribute called radius and give it the value of 1.
More commonly you might want to write your classes to be a little more flexible such that can influence the radius of the circle at the time of the creation such as:

class Circle:
    def __init__(self, radius = 1):
        self.radius = radius

which means that you can write it like

my_circle = Circle()  # has a radius of 1 as no explicit value was given
my_circle_2 = Circle(2) # has a radius of 2

- Thomas

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Sun, 12 Dec 2021 01:23:13 GMT

Hi Thomas, Thanks for your nice, valuable response.
I am new in doing the Python-ArcPy programming. I will be very careful in picking up the pecurious skills of Python syntax.
I corrected my old arcpy script and executed it. It worked nicely and I got the output.
I tried your arcpy script for the Circle class:

>>> import arcpy
>>> import os
>>> import glob 
>>> class Circle:
...     def __init__(self):
...         self.radius = 1
... my_circle = Circle()
... print (2 * 3.14 * my_circle.radius)
... my_circle.radius = 5
... print (2 * 3.14 * my_circle.radius)
... 
6.28

31.4

>>> class Circle:
...     def __init__(self, radius = 1):
...         self.radius = radius
... my_circle = Circle() #has a radius of 1 as no explicit value was given
... my_circle_2 = Circle(2) # has a radius of 2
... 
>>>

I think it worked too. But I did not see the output of the 2 circles. What should I do to get the output of the 2 circles?
Please kindly help, advise and respond again.

Many Thanks,
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ThomasEmge — Sun, 12 Dec 2021 01:23:16 GMT

Scott,

my second approach with

def __init__(self, radius = 1):

is a short hand notation that allows the user to set the radius at the time of the object creation.

radius = 1

means that when you create the object you can specify a value for the python attribute called radius. If you don't provide an explicit value then the __init__ method assumes that the radius has a value of 1.
Essentially method 1 and method 2 yield the same result:

# method 1
my_circle = Circle()
my_circle.radius = 2
# method 2
my_circle = Circle(2)

If this notation is rather confusing you then don't worry about.

As a recommendation I would suggest to stay away from classes for the moment and to revisit the concept in a couple weeks when you are feeling more at home in Python.

- Thomas

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ScottChang — Sun, 12 Dec 2021 01:23:18 GMT

Hi Thomas,
I did few trials to print the output of your arcpy script:

>>> my_circle
<__main__.Circle instance at 0x302221E8>
>>> my_circle_2
<__main__.Circle instance at 0x30222148>
>>> print my_circle
<__main__.Circle instance at 0x302221E8>

>>> return my_circle
Runtime error <type 'exceptions.SyntaxError'>: 'return' outside function (<string>, line 1)
>>> return 'my_circle'
Runtime error <type 'exceptions.SyntaxError'>: 'return' outside function (<string>, line 1)
>>> print (my_circle)
<__main__.Circle instance at 0x302221E8>

>>> print (Circle())
<__main__.Circle instance at 0x30222120>

>>> print (2 * 3.14 * my_circle)
Runtime error <type 'exceptions.TypeError'>: unsupported operand type(s) for *: 'float' and 'instance'
>>> print (2 * 3.14 * my_circle_2)
Runtime error <type 'exceptions.TypeError'>: unsupported operand type(s) for *: 'float' and 'instance'

I cannot get the decent output. Please tell me how I can get the output of your methods.

Thanks,
Scott Chang

Re: ArcGIS 10:Doing Python to check for numbers of files in a directory-indentation e

ThomasEmge — Sun, 12 Dec 2021 01:23:21 GMT

I see.

Take a look at the first line you have typed.

>>> my_circle
<__main__.Circle instance at 0x302221E8>

What this line is telling that 'my_circle' is an instance of the Circle class living at address location 0x302221E8. That is it - nothing more or less. The notion of a class is following the principles of object-oriented programming and again is not really something I would recommend to a beginner. You can google/bing/yahoo "object-oriented principles" but the findings are probably more confusing than helpful right now.

How does the Python line help you right now? Not at all.....

You want to find out what this 'my_circle' thing really is and the Python way to do that is

>>> dir(my_circle)
['__doc__', '__init__', '__module__', 'radius']

The Python dir() function will tell you more an object, its attributes and methods.
For 'my_circle' you can see that there built-in functions like __doc__, __init__, __module__ and you also find the class attribute radius. In order to find the radius of the my_circle objects you would write

>>> print my_circle.radius
1

Again my recommendation would be: don't use the class syntax -- it is over-engineering the problem. Keep it simple and use variables as of now such that:

myCircleRadius = 2
myCircleCircumference = 2 * 3.14 * myCircleRadius

- Thomas