python for the non-scripter

2013 TeachMeGIS All rights reserved.

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[email protected]

Python for the Non-Scripter

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Presentation Overview

What is Python?

Python Essentials

Extra Tidbits

Using Python in ArcMap

Label Expression

Field Calculator

Python For the Non-Scripter


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And how does it fit into ArcGIS?

What is Python?

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Python

Programming language

Object-oriented

Started in early 1990s by Guido van Rossum

Named after Monty Pythons Flying Circus

Free

Quick to learn

Easy to code

Easy to read

Many users (lots of help)

What is Python?

Why Do We Love It?


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Python and ArcGIS Desktop

Python is infiltrating ArcMap

More with each release

Label Expression

Field Calculator

Python Window

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Python Essentials


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Python the Essentials

Keywords

Special instructions

Case sensitive

Shown in blue in Python window

Examples: print

import

if

not

and

Variables

Hold a value

Set on the fly

Value sets type

Case sensitive

No keywords

Start with letter

No special characters

Functions

Action

Multiply

Concatenate

Extract

Upper case

Split a list

HINT:

Variables are objects

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Python Window

Command line window in ArcMap

Great place for practicing Python code (and getting help)


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Data Types for Variables

VARIABLE

Boolean

True

False

String

Number

Integer

Float

String

Text value

Double quotes (O&G)

Number

Integer (whole number)

Float (decimal)

Boolean

True (1)

False (0) =

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Python Syntax: Numbers

Integers and floats

Variable assignment determines type

+ - * /

Dont forget operator precedence:

Parentheses

Exponents

Multiplication, division

Addition, subtraction


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Python Syntax: Strings

Surrounded by quotes

Double

Single

Backslash (\) is a special character

Escape

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String Tools

Length

len()

Concatenation

+

Repetition

*


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Functions

Typical format: .()

hello.upper()

Use dir() to get a list of functions

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Extra Tidbits


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Directory Paths

Cannot use single backslashes in a directory path

Use:

\\

/

r

C:\\Student\\ICTPython

C:/Student/ICTPython

rC:\Student\ICTPython

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String Indexing

Square brackets [ ]

Index returns single character

0-based

Negative counts backwards from end


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String Slicing

Slice returns a substring:

2 inputs (simple)

Start, end

3 inputs (extended)

Start, end, and stride

All inputs are 0-based

Negative inputs count backwards from end

Non-inclusive

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On-the-Fly Conversion

Convert text and numeric data types on the fly:

str()

int()

float()


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Lists

Surrounded by square brackets []

Elements separated by a comma

Can contain different data types

Can be sliced and indexed like strings

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Using Python in ArcMap


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Label Expression

Switch the Parser to Python

Write the expression

Combine values

Add static strings

Add new lines

Convert values

Multiple by conversion factor

All done on-the-fly

No write access to data required

[CO_NAME] + "\n" + [PROD_CODE]

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Combination Tricks

E X P R E S S I O N R E S U LT

[PointX] + , + [PointY] 223.43, 5356.5

[County_Name] + County, +

[State]Harris County, TX

[Company] + \n + [Address]TeachMeGIS3000 Wilcrest


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Field Calculator

Switch the Parser to Python

Write the expression

Copy values

Combine values

Add strings

Convert values

Multiple by conversion factor

Change data types

QA data

Set string case

"Submerged Pile" + !OBJNAM!

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Number Tricks

E X P R E S S I O N R E S U LT

!Elevation_ft! * 0.3048 FeetMeters

!Elevation_m! * 3.2808399 Meters Feet

!Area_km2! * 247.105381 km2 Acres

!Area_acres! * 0.00404685642 Acres km2

round(!PROD! * !Royalty!, 2) $

!Part1! / !Total! %


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String Tricks

Built-in Functions

.upper()

.lower()

.title()

.replace(, )

String slicing!Company!.upper()

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Now Put it All Together

Functions

Field Values

Static Values


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SCENARIO:

Have a string formatted like: nnnn ssss ttt vvvv xxx yyyy

TASK:

Format in new field as: ttt vvvv xxx yyyy

Example: String Functions

WELL_NAME:

1200 RAAA SUA HOLY BEA CALI

NEW WELL_NAME FIELD:

SUA HOLY BEA CALI

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Example: String Functions

SOLUTION: " ".join(!WELL_NAME!.split()[2:])

WELL_NAME Column with original data1200 RAAA SUA HOLY BEA CALI

!WELL_NAME!.split()

Splits the string at the spaces and puts the pieces in a list

1200, RAAA, SUA , HOLY,BEA, CALI

!WELL_NAME!.split()[2:]

Removes the first 2 values from the list

SUA , HOLY,BEA, CALI

.join()Creates a string from the values in separated by a space

SUA HOLY BEA CALI


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Help and Resources

Learning Python

Python in a Nutshell

Books

http://support.esri.com

http://resources.arcgis.com

http://www.python.org

http://www.diveintopython.org

Websites

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Show Codeblock

Advanced Calculations


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Show Codeblock Calculations

Write function in Pre-Logic Script Code section

Call function (with inputs) in Expression section

Returned value is written to the table

Expression

Function

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Pick Non-Null Value

TASK:

Populate a column with either API or UWI (whichever exists)

PickNonNullString(str(!API!), str(!UWI!))

def PickNonNullString(val1, val2):valOut = val2if val1:valOut = val1

return valOut


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Any questions?

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