CSCI 1101B Introduction to Python Mohammad T . Irfan New office - - PDF document
2/12/2014 CSCI 1101B Introduction to Python Mohammad T . Irfan New office hours: M 10-12, Th 3-5 2/4/14 Basic Elements of Python 1 2/12/2014 Statement print Welcome to Python print Whats your name? total = 0
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print ‘Welcome to Python’ print “What’s your name?” total = 0 x = [10, 20, 5] for number in x: total = total + number print total
Header Body – must use indentation
Function name Parameters
More on functions later
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Scalar – 4 types
int (example: -10000, 200, 53) float (example: -37.59, 28.0) bool (example: True, False) None
Non-scalar
String (example: “hello”, “57”) And many other ... (You will define and create
your own non-scalar objects later on)
Arithmetic
x + y x – y x * y x/y
Caution: when x and y are both int, then the result is
also int (Python 2.7 truncates all decimal digits after the decimal point) – it’s called “integer division”
Better practice: Use x//y when x and y are both int
// operator specifically means integer division
x % y: remainder of the division x/y for int x & y x ** y: x raised to the power y comparison: == (equal), != (not eq), >, >=, <, <=
Precedence – usual
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Logical operators (on bool)
a and b a or b not a
Variable: named storage space
def area(): pi = 3.14159 r = 10 area = pi * r**2 print area
You don’t need to specify type of a variable –
it’s automatically determined
Naming a variable
Must start with a letter (upper or lower case) or _,
may contain digits
Use sensible names. Cannot use reserved words.
Note the indentation
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An if block can be optionally
Note the indentation
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if block, followed by any number of elif blocks,
followed by an optional else block def showMinimum(x, y, z): if x < y and x < z: print x, 'is min' elif y < z: print y, 'is min' else: print z, 'is min‘
Note: parameter passing to a function To “call” this function from JES, load it first and
then enter the following command into the black window
showMinimum (20, 30, 5)
if statements can be nested
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12
Integers Floats Strings
31,364
0.01 12.998 34,654.01 1.01 Mark Bowdoin College 85 5th Street NW Inside the computer, these are all just bits
What would be the output of the following?
print 1/2
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>>> print 12 * 3 36 >>> value = 12 >>> print value 12 >>> print value * 3 36 >>> name = "Mark" >>> print name Mark >>> print name * 3 MarkMarkMark >>> print "Mark" * 3 MarkMarkMark
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Examples
“Hello and welcome” “Bowdoin College”
Assignment statement
college = “Bowdoin College”
Main difference is representation You can apply all arithmetic operators on 57
57 + 2 57 * 2
Arithmetic operations are meaningless for
“57”
“57” + 2
# ERROR
“57” * 2
# ‘5757’
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college = “Bowdoin College” Length of a string
len(college)
# 15 Indexing
college[2]
# ‘w’
college[-1]
# ‘e’
college[-2]
# ‘g’ Slicing
college[0:2]
# ‘Bo’
college[0:len(college)]
# ‘Bowdoin College’ Splitting
college.split()
# ['Bowdoin', 'College']
x = raw_input (‘Enter your name’) y = raw input (‘How old are you?’)
Suppose user enters 20 as his/her age y’s value is “20”, not 20 if you want to convert string “20” to number 20,
y = int(y) # Can use a different variable name on LHS
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General form (not actual code)
for loop_variable in sequence:
body of for loop
Visualization of for loop
Use boxes to replace the for loop
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sequence is commonly specified using the
built-in range function with 3 parameters:
start (optional, default is 0) end (must, actually ends before this value) increment (optional, default is 1)
Examples
range(10, 70, 20)
# [10, 30, 50]
range (0, 5, 1)
# [0, 1, 2, 3, 4]
range (0, 5)
# [0, 1, 2, 3, 4]
range (5)
# [0, 1, 2, 3, 4]
Caution: integer division!
Better to write: avg = float(total)/len(x)
Loop variable: Choose any name you want