Merge pull request swcarpentry#34 from pipitone/swc_exercises

Exercises from the Software Carpentry 4.0 website

python/data_structures/exercises/setdict_dependencies.txt

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+# Sample dependencies for Danielle's package manager
+# aside: these are actually taken from real projects
+#
+# Format: [package][TAB][dependency]
+segtools	numpy
+segtools	latticeextra
+segtools	reshape
+segtools	rpy2
+segtools	r
+segtools	genomedata
+segtools	pygraphviz
+segtools	xorg
+segtools	python
+genomedata	hdf5
+genomedata	numpy
+genomedata	pytables
+genomedata	python
+pytables	numpy
+pytables	hdf5
+pytables	numexpr
+pytables	cython
+pytables	python
+hdf5	zlib
+hdf5	gcc
+numpy	lapack
+numpy	gcc
+numpy	python-nose
+numpy	gfortran
+numpy	python
+segway	gmtk
+segway	sge
+segway	hdf5
+segway	numpy
+segway	drmaa
+segway	pytables
+segway	python
+# [package][TAB][package] allows for spaces in package names
+# Make sure you split on tab, not on all whitespace
+drmaa	lsf drmaa
+pygraphviz	graphviz
+pygraphviz	python
+latticeextra	lattice
+latticeextra	rcolorbrewer
+latticeextra	grid
+reshape	plyr
+rpy2	python
+xorg	libxss
+xorg	zlib
+xorg	freetype
+lattice	grid
+lattice	grdevices
+lattice	graphics
+lattice	stats
+lattice	utils
+plyr	itertools
+plyr	iterators
+itertools	foreach
+iterators	utils
+graphviz	libpangocairo
+libpangocairo	cairo
+libpangocairo	freetype
+libpangocairo	fontconfig
+libpangocairo	glib
+cairo	libpng
+libpng	zlib

python/intro/exercises/python.markdown

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+The following exercises do not contain solutions.  Yet.  Instead, we will be
+asking you to submit your solutions to these exercises and then we will post up
+solutions at the start of next week.  We encourage you to discuss your
+approaches or solutions on the course forum!
+
+To submit your exercises, please create a `python` folder in your personal
+folder in the course repository.  Place all of the code and files for theses
+exercises in that folder and be sure to check it in. 
+
+## Exercise 1: Short Problems
+
+
+1. Write a bullet list description of what happens when Python evaluates the
+statement `x += x - x` when `x` starts with the value 3.  Submit your answer in
+a file called `evaluation.txt`.
+
+2. In the United States, a car's fuel efficiency is measured in miles per
+gallon.  In the metric system, it is usually measured in liters per 100
+kilometers.
+
+  1. Write a function called `convert_mileage` that converts from miles per
+  gallon to liters per 100 kilometers.
+
+
+  2. Test that your functions returns the right values for 20 and 40 miles per
+  gallon.
+
+
+  3. How did you figure out what the right value was?  How closely do the
+  computer's results match the ones you expected?
+
+
+  Submit your answer in a file called `mileage.py` (for part 1) and
+  `mileage.txt` (for part 3).
+
+3. The expression `1+'a'` is not legal in Python because 1 is a number and 'a'
+is a string.  Do you think `1<'a'` is legal or not?  If it is legal, what is its
+value, and why?  Submit your answer in a file called `comparison.txt`.
+
+4. What is the value of each of the following expressions, and why? Submit your
+answer in a file called `boolean.txt`.
+  1. `True and not False`
+  2. `True or True and False`
+  3. `not True or not False`
+  4. `True and not 0`
+  5. `52 < 52.3`
+  6. `1 + 52 < 52.3`
+  7. `4 != 4.0`
+
+5. Here is a possible definition of how `and` works:
+
+   > If both operands are true, `and`'s result is its second value. If either is
+   > false, `and`'s result is `False`.
+
+   Is this the rule that Python actually uses?  If not, provide a counter example.
+   Submit your answer in a file called `and.txt`.
+
+6. You want an automatic wildlife camera to switch on if the light level is less
+than 0.01 or if the temperature is above freezing, but not if both conditions
+are true.  Your first attempt to write this is as follows:
+
+   ```python    
+       if (light < 0.01) or (temperature > 0.0):
+          if (light < 0.01) and (temperature > 0.0):
+              pass
+          else:
+              camera.on()
+   ```
+
+   A friend says that you could write this more simply as follows:
+
+   ```python    
+       if (light < 0.01) != (temperature > 0.0):
+          camera.on()
+   ```
+
+   Is your friend right?  If so, explain why.  If not, give values for `light` and
+   `temperature` that will produce different results for the two fragments of code.
+   Either way, which do you find easier to understand, and why?  Submit your answer
+   in a file called `wildlife.txt`.
+
+
+## Exercise 2: Viewing Grades
+
+A post-doc is teaching a biology course for the first time.  The university's
+learning management system is "temporarily unavailable" while the system
+administrators try to undo a recent upgrade, so the post-doc has to manage marks
+herself for the foreseeable future.  She needs a program to help her see:
+  * a list of all students with their marks;
+  * the highest mark;
+  * the lowest mark; and
+  * the average mark.
+
+Grades for each assignment are stored in a separate file.  Each file is
+formatted like this:
+    aturing: 86
+    inewton: 67.5
+    cdarwin: 90
+    fnightingale: 99
+    cvraman: 10
+
+Write four functions that work as follows:
+  1. `grade_show('ex3.dat', 'inewton')`: print inewton's grade in `ex3.dat`
+  2. `grade_highest('ex3.dat')`: print the highest grade in `ex3.dat`
+  3. `grade_lowest('ex3.dat')`: print the lowest grade in `ex3.dat`
+  4. `grade_average('ex3.dat')`: print the average grade in `ex3.dat`
+
+You may assume that all students' IDs are unique.  Submit your solution in a
+file called `grade1.py`.  Please also submit a plain text file called
+`grade1.txt` that explains ambiguities or omissions there are in this
+specification, i.e., what do you have to implement that someone else might
+reasonably implement differently?
+
+## Exercise 3: Managing Grades
+
+The post-doc also needs to be able to:
+  * add a new student with a grade;
+  * change a student's mark; and
+  * remove a student
+
+Create and submit another file called `grade2.py` containing functions that work
+as follows:
+  1. `grade_create('ex3.dat')`: create an empty grades file
+  2. `grade_add('ex3.dat', 'inewton', 58)`: set inewton's grade in `ex3.dat` to
+     58
+  3. `grade_change('ex3.dat', 'inewton', 88)`: change inewton's grade in
+     `ex3.dat` to 88
+  4. `grade_remove('ex3.dat', 'inewton')`: remove inewton's grade from `ex3.dat`
+
+
+## Exercise 4: Steganography
+
+_Steganography_ is the art or science of hiding secret messages in plain sight.
+For example, the first letter of every fifth line of the original edition of The
+Tempest might spell out "Francis Bacon writ Shakesprs plays", or we could
+introduce deliberate misspellings into an email message such that every wrong
+letter, taken together, spelled out "Higgs Boson found".
+
+Write a program that takes a short message and a positive integer N as
+arguments, reads in a text file, and writes out the text with every N'th letter
+changed to encode the message.  For example, suppose the file `example.txt`
+contains:
+
+```
+Since 1997, Software Carpentry has taught scientists and engineers the concepts,
+skills, and tools they need to use and build software more productively. All of
+the content is freely available under a Creative Commons license, and we are
+constantly adding and updating lectures, videos, and exercises.
+```
+
+If the program is run as:
+> `python steg.py "Hacker Within" 5 example.txt`
+
+then the output should be:
+
+```
+Hincea1997c SofkwareeCarprntry has Waughiscitntishs ani engnneers the concepts,
+skills, and tools they need to use and build software more productively. All of
+the content is freely available under a Creative Commons license, and we are
+constantly adding and updating lectures, videos, and exercises.
+```
+
+Submit your solution in a file called `steg.py`.  Please also create a plain
+text file called `steg.txt` containing answers to the following questions:
+
+  1. What ambiguities or omissions are there in this specification? I.e., what
+  do you have to implement that someone else might reasonably implement
+  differently?
+
+  2. This program's output is clearly garbled.  One way to make that less
+  obvious is to increase the spacing between changes.  What are some others?
+
+
+  3. How did you test your program?  How confident are you that it works
+  correctly?  How confident do you think someone else could be that it works
+  correctly?