1. Geography 465 Assignments, Conditionals, and Loops

2. Assignments in Python Assignment target on left of ‘=‘ and assignment object is on right fc = “C:\\ProjectData\\SanDiego.mdb\\Freeways.shp” Remember, variables are case sensitive fc = “Freeways.shp” Fc = 20000 Remember, variables can hold different data types –numbers, strings, lists, files

3. Review: Variable naming conventions Upper case versus lower case –First word lower case, capitalize each successive word tableFieldName = “Street” - Acronym at the beginning, use lower case letters gdbPath = “C:\\SanDiego.mdb” -Acronym in the middle or at the end, use upper case letters inputFC = “Streets.shp” Avoid special characters (for example / \ & % # !) Use descriptive variable names

4. Comparison: Boolean Expressions A boolean expression is an expression that is either true or false. In Python an expression that is true has the value 1, and an expression that is false has the value 0. In this case the equal comparison (not assignment) operator is as follows. >>> 5 == 5 1 >>> 5 == 6 0

5. Boolean Expressions The == operator is one of the comparison operators; the others are: x != y # x is not equal to y x > y # x is greater than y x < y # x is less than y x >= y # x is greater than or equal to y x <= y # x is less than or equal to y

6. Logical Operators There are three logical operators: and, or, and not. The semantics (meaning) of these operators is similar to their meaning in English. For example, x > 0 and x < 10 is true only if x is greater than 0 and less than 10.

7. Conditional Decision Statement Conditional statement: if…elif…else if x == 1: print “x is 1” elif x == 2: print “x is 2” else: print “x is not 1 or 2” Colons are used at the end of each condition Indentation defines what executes for each condition

8. Looping - 1 While loop x = 1 while x < 10: print x x = x + 1 Colons used at end of each statement Indentation defines what executes for the loop

9. Looping - 2 Counted loop for x in range(1, 5): print x Counted loops increment and test a variable on each iteration of the loop The last value is not executed

10. Looping - 3 List loop x = [1, 2, 3] For a in x: print a List loops iterate over each value in a list The loop will execute once for each value in the list