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--- python:dierbach:chapter_2_data_and_expressions [2016/07/28 20:42] – created mithat
+++ python:dierbach:chapter_2_data_and_expressions [2016/07/29 01:46] – mithat
@@ Line 3: / Line 3: @@
 ====== Data and Expressions ======
+Mithat Konar\\
+based on Dierbach's //[[http://www.wiley.com/WileyCDA/WileyTitle/productCd-EHEP002046.html|Introduction to Computer Science using Python]]//.
 ===== Contents =====
@@ Line 14: / Line 16: @@
 ===== Literals =====
-{{http://lorempixel.com/480/360/cats}}
+{{http://mkonar.org/assets/img/cat-silhouette-01-trans-64px.png}}
 ===== What is a literal? =====
@@ Line 160: / Line 161: @@
 ===== Variables and Identifiers =====
-{{http://lorempixel.com/480/360/cats}}
+{{http://mkonar.org/assets/img/cat-silhouette-01-trans-64px.png}}
 ===== What is a variable? =====
+  * **variable**: a name associated with a value.
+<code>
+       +--------+
+num -->|   10   |
+       +--------+
+</code>
+===== Assignment =====
+  * **assignment**: take the value resulting from the expression on the right and copy it into the variable on the left.
+  * **assignment operator**: ''%%=%%'' in Python.
+    * ''%%=%%'' is //not// “equals”!
+<code python>
+foo = 7
+num = 1 + foo
+foo = foo + 1
+</code>
+===== Variable reassignment =====
+<code python>
+num = 10    #        +--------+
+k = num     # num -->|   10   |
+            #   k -->|        |
+            #        +--------+
+</code>
+<code python>
+k = 20      #        +--------+
+            # num -->|   10   |
+            #        +--------+
+            #        +--------+
+            #   k -->|   20   |
+            #        +--------+
+</code>
+===== id() =====
+  * Use ''%%id()%%'' to see if two variables are pointing to the same thing.
+<code python>
+>>> num = 10
+k = num
+>>> id(num)
+??? # some number
+>>> id(k)
+??? # same number as above
+k = 20
+>>> id(num)
+??? # same as before
+>>> id(k)
+??? # different
+</code>
+===== What is an identifier? =====
+  * **identifier**: a sequence of one or more characters used to provide a name for a given program element.
+  * **identifier**: names of things.
+  * Rules of the name:
+    * letters, digits, and the underscore character only (no spaces)
+    * can’t start with a digit
+    * don’t use underscore for the first character for now
+    * can be as long as you want
+===== Keywords and help =====
+  * **keyword** an identifier that has predefined meaning in a programming language.
+  * You can’t use a keyword as your own identifier in Python.
+  * Get a list of keywords:
+<code python>
+>>> help()
+help> keywords
+# table of keywords appears
+help> quit
+>>>
+</code>
+  * Things you think should be keywords are not!
+  * Check “special” words using ''%%'testword' in dir(__builtins__)%%''
+===== Example: Restaurant Tab Calculation =====
+RestaurantTab.py
+<code python>
+# Restaurant Tab Calculation Program
+# This program will calculate a restaurant tab with a gift certificate
+# initialization
+tax = 0.08
+# program greeting
+print('This program will calculate a restaurant tab for a couple with')
+print('a gift certificate, with a restaurant tax of', tax * 100, '%\n')
+# get amount of gift certificate
+amt_certificate = float(input('Enter amount of the gift certificate: '))
+# cost of ordered items
+print('Enter ordered items for person 1')
+appetizer_per1 = float(input('Appetizier: '))
+entree_per1 = float(input('Entree: '))
+drinks_per1 = float(input('Drinks: '))
+dessert_per1 = float(input('Dessert: '))
+print('\nEnter ordered items for person 2')
+appetizer_per2 = float(input('Appetizier: '))
+entree_per2 = float(input('Entree: '))
+drinks_per2 = float(input('Drinks: '))
+dessert_per2 = float(input('Dessert: '))
+# total items
+amt_person1 = appetizer_per1 + entree_per1 + drinks_per1 + dessert_per1
+amt_person2 = appetizer_per2 + entree_per2 + drinks_per2 + dessert_per2
+# compute tab with tax
+items_cost = amt_person1 + amt_person2
+tab = items_cost + items_cost * tax
+# display amount owe
+print('\nOrdered items: $', format(items_cost, '.2f'))
+print('Restaurant tax: $', format(items_cost * tax, '.2f'))
+print('Tab: $', format(tab - amt_certificate, '.2f'))
+print('(negative amount indicates unused amount of gift certificate)')
+</code>
+===== Operators =====
+{{http://mkonar.org/assets/img/cat-silhouette-01-trans-64px.png}}
+===== What Is an Operator? =====
+**operator**: a symbol that represents an operation that may be performed on one or more operands. **binary operator**: takes two operands **unary operator**: takes one operand
+===== Arithmetic operators =====
+^Operator  ^               ^Example       ^Result  ^
+|-x        |negation       |-10           |-10     |
+|x + y     |addition       |10 + 25       |35      |
+|x - y     |subtraction    |10 - 25       |-15     |
+|x * y     |multiplication |10 * 5        |50      |
+|x / y     |division       |25 / 10       |2.5     |
+|x %%//%% y|truncating div.|25 %%//%% 10  |2       |
+|x % y     |modulus        |25 % 10       |2.0     |
+|x %%**%% y|exponentiation |10 %%**%% 2   |100     |