Advanced scripting programming

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Advanced scripting programming

• jesus.ibanez_at_upf.edu

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Assignment

• spam 'Spam' Basic form
• spam, ham 'yum', 'YUM' Tuple assignment
  (positional)
• spam, ham 'yum', 'YUM' List assignment
  (positional)
• spam ham 'lunch' Multiple-target

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Assignment

• nudge 1
• wink 2
• A, B nudge, wink tuples
• A, B
• (1, 2)
• C, D nudge, wink lists
• C, D
• (1, 2)
• nudge, wink wink, nudge tuples
  swaps values
• nudge, wink
• (2, 1)

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Variable name rules

• Syntax
• (underscore or letter) (any number of letters,
  digits, or underscores)
• Case matters
• SPAM is not the same as spam
• Reserved words are off limits
• print, and, while, etc

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Input

• Function raw_input() designed to read a line of
  input from the user. 1 optional argument string
  to prompt user
• mystr raw_input("Enter a string")
• Enter a stringHello World!
• mystr
• 'Hello World!'

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Input

• If int or float desired, simply convert string
• int(mystring)-convert to int (if possible)
• float(mystring)-convert to float (if possible)
• a int(raw_input("Enter an integer "))
• Enter an integer 123
• a
• 123

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Output

• print spam, ham Print objects to sys.stdout, add
  a space between
• print spam, ham, Same, but don't add newline at
  end
• print "a", "b"
• a b
• print "a" "b"
• ab
• print "s...s" ("a", "b")
• a...b

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Output

• print 'hello world' print a
  string object
• hello world
• 'hello world'
  interactive prints
• 'hello world'
• import sys
  printing the hard way
• sys.stdout.write('hello world\n')
• hello world

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Relational and logical operators

• Relational operators
•  
• equal
• !, not equal
• greater than
• greater than or equal

• Logical operators
• and
• or
• not

• True means any nonzero number or nonempty object.
• False means not true a zero number, empty
  object, or None.

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Control of flow

• Sequential
• Conditional if
• Iterative while, for

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Decision making statements
if
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Decision making statements
if elif
else

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Decision making statements

• example
• if 1
• ... print 'true'
• ...
• true
• if not 1
• ... print 'true'
• ... else
• ... print 'false'
• ...
• false

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Decision making statements

• example
• x 'killer rabbit'
• if x 'roger'
• ... print "how's jessica?"
• ... elif x 'bugs'
• ... print "what's up doc?"
• ... else
• ... print 'Run away! Run away!'
• ...
• Run away! Run away!

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Decision making statements

• example
• if choice 'spam'
• ... print 1.25
• ... elif choice 'ham'
• ... print 1.99
• ... elif choice 'eggs'
• ... print 0.99
• ... elif choice 'bacon'
• ... print 1.10
• ... else
• ... print 'Bad choice'
• ...
• 1.99

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Decision making statements

• choice 'ham'
• print 'spam' 1.25,
• ... 'ham' 1.99,
• ... 'eggs' 0.99,
• ... 'bacon' 1.10choice
• 1.99
• a dictionary-based 'switch',
• use has_key() test for default case

• example
• if choice 'spam'
• ... print 1.25
• ... elif choice 'ham'
• ... print 1.99
• ... elif choice 'eggs'
• ... print 0.99
• ... elif choice 'bacon'
• ... print 1.10
• ... else
• ... print 'Bad choice'
• ...
• 1.99

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Decision making statements
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Decision making statements

• x 1
• if x
• y 2
• if y
• print 'block2'
• print 'block1'
• print 'block0'

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Program looping
while
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Program looping
while else

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Program looping

• example
• while 1
• ... print 'Type Ctrl-C to stop me!'

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Program looping

• example
• x 'spam'
• while x
• ... print x,
• ... x x1 strip first character
  off x
• ...
• spam pam am m

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Program looping

• example
• a0 b10
• while a loops
• ... print a,
• ... a a1
• ...
• 0 1 2 3 4 5 6 7 8 9

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Program looping

• break
• Jumps out of the closest enclosing loop (past the
  entire loop statement).
• continue
• Jumps to the top of the closest enclosing loop
  (to the loop's header line).
• pass
• Does nothing at all it's an empty statement
  placeholder.
• loop else block
• Run if and only if the loop is exited
  normallyi.e., without hitting a break.

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Program looping
while if
break if continue else

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Program looping

• example
• while 1 pass type Ctrl-C to stop me!

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Program looping

• example
• x 10
• while x
• x x-1
• if x 2 ! 0 continue odd?--skip print
• print x,

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Program looping

• example
• x y / 2
• while x 1
• if y x 0 remainder
• print y, 'has factor', x
• break skip else
• x x-1
• else normal exit
• print y, 'is prime'

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Program looping
for in
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Program looping
for in else

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Program looping
for in
if break if continue else

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Program looping

• example
• for x in "spam", "eggs", "ham"
• ... print x,
• ...
• spam eggs ham

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Program looping

• example
• sum 0
• for x in 1, 2, 3, 4
• ... sum sum x
• ...
• sum
• 10
• prod 1
• for item in 1, 2, 3, 4 prod prod item
• ...
• prod
• 24

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Program looping

• example
• S, T "lumberjack", ("and", "I'm", "okay")
• for x in S print x,
• ...
• l u m b e r j a c k
• for x in T print x,
• ...
• and I'm okay
• T (1, 2), (3, 4), (5, 6)
• for (a, b) in T
  tuple assignment at work
• ... print a, b
• ...
• 1 2
• 3 4
• 5 6

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Program looping

• example
• items "aaa", 111, (4, 5), 2.01
  a set of objects
• tests (4, 5), 3.14
  keys to search for
• for key in tests
  for all keys
• ... for item in items
  for all items
• ... if item key
  check for match
• ... print key, "was found"
• ... break
• ... else
• ... print key, "not found!"
• ...
• (4, 5) was found
• 3.14 not found!

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Program looping

• example
• for key in tests for all keys
• ... if key in items let Python
  check for a match
• ... print key, "was found"
• ... else
• ... print key, "not found!"
• ...
• (4, 5) was found
• 3.14 not found!

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Program looping

• example
• seq1 "spam"
• seq2 "scam"
• res start empty
• for x in seq1 scan first
  sequence
• ... if x in seq2 common item?
• ... res.append(x) add to result
  end
• ...
• res
• 's', 'a', 'm'

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Program looping

• example
• file open("name", "r")
• while 1
• line file.readline() fetch next line,
  if any
• if not line break exit loop on
  end-of-file
• Process line here

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Program looping

• example
• file open("name", "r")
• for line in file.readlines() read into a
  lines list
• Process line here

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Range and counter loops

• example
• range(5), range(2, 5), range(0, 10, 2)
• (0, 1, 2, 3, 4, 2, 3, 4, 0, 2, 4, 6, 8)

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Range and counter loops

• example
• X 'spam'
• for item in X print item,
  simple iteration
• ...
• s p a m

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Range and counter loops

• example
• i 0
• while i iteration
• ... print Xi, i i1
• ...
• s p a m

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Range and counter loops

• example
• for i in range(len(X)) print Xi,
  manual indexing
• ...
• s p a m

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Range and counter loops

• example
• for i in range(3) print i, 'Pythons'
• ...
• 0 Pythons
• 1 Pythons
• 2 Pythons

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Exercises

• Try to translate some of your C or Perl programs
  into Python ones.