Differences

This shows you the differences between two versions of the page.

--- python:dierbach:chapter_2_data_and_expressions [2016/07/28 21:03] – mithat
+++ python:dierbach:chapter_2_data_and_expressions [2016/07/29 01:46] – mithat
@@ Line 1: / Line 1: @@
 ~~SLIDESHOW~~
 ~~NOTOC~~
+====== 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 12: / Line 16: @@
 ===== Literals =====
-<HTML>
+{{http://mkonar.org/assets/img/cat-silhouette-01-trans-64px.png}}
-<iframe width="560" height="315" src="https://www.youtube.com/embed/pxf_EVTJtPg" frameborder="0" allowfullscreen>
-</iframe>
-</HTML>
 ===== What is a literal? =====
   * **literal**: a sequence of one or more characters that stands for itself.
-  * **numeric literal**: contains only the digits 0â€“9, a sign character (1 or 2) and a optional decimal point.
+  * **numeric literal**: contains only the digits 0–9, a sign character (1 or 2) and a optional decimal point.
     * integer versus floating point value
     * ''%%e%%'' for scientific notation
@@ Line 27: / Line 29: @@
   * Floating point values have limited range and precision.
-  * IEEE 754: Â±10<sup>-308</sup> to Â±10<sup>308</sup> with 16 to 17 digits of precision.
+  * IEEE 754: ±10<sup>-308</sup> to ±10<sup>308</sup> with 16 to 17 digits of precision.
-  * **arithmetic overflow**: results when operation causes number to be â€œtoo bigâ€.
+  * **arithmetic overflow**: results when operation causes number to be “too big”.
 <code python>
@@ Line 34: / Line 36: @@
 inf
 </code>
-  * **arithmetic underflow**: results when operation causes number to be â€œtoo smallâ€.
+  * **arithmetic underflow**: results when operation causes number to be “too small”.
 <code python>
@@ Line 133: / Line 135: @@
       'Number of Credits:', total_credits, 'GPA:', current_gpa)
 </code>
-  * Doesnâ€™t work to break up a string.
+  * Doesn’t work to break up a string.
 ===== Explicit Line Joining =====
-  * **explicit joining** (backslash) can be used in some situations where implicit joining wonâ€™t.
+  * **explicit joining** (backslash) can be used in some situations where implicit joining won’t.
 <code python>
@@ Line 143: / Line 145: @@
               num_minutes * 60
 </code>
-  * Also doesnâ€™t work to break up strings.
+  * Also doesn’t work to break up strings.
 ===== Silly encoding example =====
@@ Line 159: / Line 161: @@
 ===== Variables and Identifiers =====
-<HTML>
+{{http://mkonar.org/assets/img/cat-silhouette-01-trans-64px.png}}
-<iframe width="560" height="315" src="https://www.youtube.com/embed/pxf_EVTJtPg" frameborder="0" allowfullscreen>
-</iframe>
-</HTML>
 ===== 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     |