Book Cover

Chapter 12

A Few More Things About Programming

Note: The examples below are abridged; the book contains more details.

  1. Git
  2. Subversion
  3. Ant
  4. Exceptions
  5. Handling Exceptions - Part I
  6. Handling Exceptions - Part II
  7. Handling Exceptions - Part III
  8. Handling Exceptions - Part III
  9. Docstrings
  10. Debugging

Git

# Example 1 - config
git config --global user.name "John Smith"
git config --global user.email "[email protected]"

# Example 2 - init
# change to parent directory where repository should lie
cd dir_name
# create a new directory representing repository
git init respository_name
# enter directory representng new repository
cd respository_name

# Example 3 - add
touch new_file  # create an empty file
git add new_file  # add new file to staging area
git commit -m "demo commit: adding an empty file new_file"

# Example 4 - status
git status

# Example 5 - another commit
echo 123456 >>! new_file  # add some text to empty file
# commit new version of new_file
git commit -m "added 123456 to file" new_file

# Example 6 - another commit
git commit -a -m "updating multiple files"

# Example 7 - branch
git branch new_branch  # create a new branch
git branch  # list all branches

# Example 8 - rev-parse
git rev-parse master~2 # display SHA-1 codename
git rev-parse --short master~2 # display shortened SHA-1 codename

# Example 9 - reverts to the previous version
git init demo_repos
cd demo_repos
echo 123 > demo_file
git add demo_file
git commit -a -m "adding demo_file containing 123"
echo 456 >>! demo_file
git commit -a -m "adding 456 to demo_file"
cat demo_file
git checkout master~1  # change version to previous version
cat demo_file

# Example 10 - merge
git branch feature1
git checkout feature1 ## Switched to branch 'feature1'
echo abc > feature_file
git add feature_file
git commit -a -m "added feature_file with abc"
git checkout master ## Switched to branch 'master'
git merge feature1  # merge feature1 branch into master
ls  # both files appear in master after the merge

# Example 11 - rebase
git checkout feature1
git rebase master  # rebase master into feature1 branch

# Example 12 - clone
git clone ssh://[email protected]/path/projectName.git

# Example 13 - log
git log | head

# Example 14 - diff
git diff master~1 master | head

Subversion

# Example 1 - copy
svn copy trunk path-to-branch/branch_name

# Example 2 - merge
svn merge path-to-branch/branch_name

Ant

<?xml version="1.0"?>
<project name="hello" default="build">
  <target name="build" description="build project">
    <mkdir dir="classes"/>
    <javac destdir="classes">
      <src path="src"/>
    </javac>
  </target>
  <target name="clean" description="clean class files">
    <delete>
      <fileset dir="classes">
        <include name="*.class"/>
      </fileset>
    </delete>
  </target>
</project>

Exceptions

import math

def foo(x):
  if not isinstance(x, int):
    raise TypeError("arguments to foo must be integers")
  if x <= 0:
    raise ValueError("arguments to foo must be positive")
  return(x + math.log(x))


foo(-3)  # exception triggered and program halted 
foo(3)  # never executed

Handling Exceptions - Part I

import math

def foo(x):
  if not isinstance(x, int):
    raise TypeError("arguments to foo must be integers")
  if x <= 0:
    raise ValueError("arguments to foo must be positive")
  return(x + math.log(x))


try: 
  foo(-3)  # exception triggered and program halted 
  foo(3)  # never executed
except: 
  print("exception in sequence of foo() calls")
print("program resumes execution and is not terminated")

Handling Exceptions - Part II

import math

def foo(x):
  if not isinstance(x, int):
    raise TypeError("arguments to foo must be integers")
  if x <= 0:
    raise ValueError("arguments to foo must be positive")
  return(x + math.log(x))

try: 
  foo(-3)  # exception triggered and program halted 
  foo(3)  # never executed
except TypeError:  # handle TypeError exceptions
  print("Incorrect Type in sequence of foo() calls")
except ValueError:  # handle ValueError exceptions
  print("Non-positive value in sequence of foo() calls")
else: 
  print("no exceptions handled")  
finally:
  print("always handled")  
print("program resumes execution and is not terminated")

Handling Exceptions - Part III

import math

def foo(x):
  if not isinstance(x, int):
    raise TypeError("arguments to foo must be integers")
  if x <= 0:
    raise ValueError(f"arguments to foo must be positive: {x}")
  return(x + math.log(x))


try: 
  foo(-3)  # exception triggered and program halted 
  foo(3)  # never executed
except TypeError:  # handle TypeError exceptions
  print("Incorrect Type in sequence of foo() calls")  
except ValueError as e:  # handle ValueError exceptions
  print("Non-positive value in sequence of foo() calls:")
  print(e.args)
print("program resumes execution and is not terminated")

Handling Exceptions - Part III

import math

# Custom exception: either type or value error
class InvalidTypeOrValueError(Exception):
  def __init__(self, a_val, a_type):  # custom constructor
    # calls super class constructor (Python 3 syntax)
    super().__init__("incorrect type and value. " + 
      "val: " + str(a_val) + " " + "type: " + str(a_type))
    self.val = a_val
    self.type = a_type


def foo(x):
  if not isinstance(x, int) or x<=0:
    raise InvalidTypeOrValueError(x,type(x))
  return(x + math.log(x))


try: 
  foo(-3) 
  foo(3)
except InvalidTypeOrValueError as e:
  print("Incorrect type or value in sequence of foo() calls: ")
  print(e.args)

Docstrings

class Point(object):
  "A point in a two-dimensional space"

  def __init__(self, x=0, y=0):
    """
    Initializes the point object to the origin by default,
    or otherwise the initializes to the passed x,y arguments.
    """
    self.x = x
    self.y = y
  def __del__(self):
    "Prints a message when an object is destroyed."
    print("destructing a point object")
  def displayPoint(self):
    "Prints the object by displaying its x and y coordinates."
    print("x: %f, y: %f" % (self.x, self.y))


help(Point)  # shows class doctring
help(Point.displayPoint)  # shows method docstring

Debugging

# Example 1
foo2 = function(i) {
  a = i + 1;
  b = a + 1;
  browser();
  a = b + 1;
  return(b)
}
foo2(3)

# Example 2
foo3 = function(i) {
  a = i + 1;
  b = a + 1;
  a = b + 1;
  return(b)
}
debug(foo3)
foo3(1)
undebug(foo3)

# Example 3
# start profiling
Rprof("diagonsisFile.out")
A = runif(1000)  # generate a vector of random numbers in [0,1]
B = runif(1000)  # generate another random vector
C = eigen(outer(A,B))
Rprof(NULL)  # end profiling
summaryRprof("diagonsisFile.out")