Python Programming Presentation

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Reading from the text console[edit]

User input can be read from the keyboard with or without a message text. The value returned is always a string:

a = raw_input()
a = raw_input('Please enter a number')

Writing to the text console[edit]

The Python print statement is very versatile and accepts almost any combination of strings, numbers, function calls, and arithmetic operations separated by commas.

print 'Hello World'
print 3 + 4
print 3.4
print ”””Text that stretches over
multiple lines.”””
print 'number', 77
print int(a) * 7

String formatting[edit]

Variables and strings can be combined, using formatting characters. This works also within a print statement. In both cases, the number of values and formatting characters must be equal.

s = 'Result: %i'%(number)
print 'Hello %s!'%('Roger')
print '(%6.3f/%6.3f)'%(a,b)

The formatting characters include:

  •  %i – an integer.
  •  %4i – an integer formatted to length 4.
  •  %6.2f – a float number with length 6 and 2 after the comma.
  •  %10s – a right-oriented string with length 10.

Escape characters[edit]

Strings may contain also the symbols: \t (tabulator), \n (newline), \r (carriage return), and \\ (backslash).

Determining the length of sequences[edit]

The len() functions returns an integer with the length b of an argument. It works with strings, lists, tuples, and dictionaries.

l = [0,1,2,3]
print len(l) # → 4

Creating lists of integer numbers[edit]

The range function allows to create lists of numbers on-the-fly. There are two optional parameters for the start value and the step size.

l = range(4) # [0,1,2,3]
l = range(1,5) # [1,2,3,4]
l = range(2,9,2) # [2,4,6,8]
l = range(5,0,-1) # [5,4,3,2,1]

Summing up numbers[edit]

The sum of a list of integer or float numbers can be calculated by the sum() function.

l = [1,2,3,4]
print sum(l)

Enumerating elements of lists[edit]

The enumerate() function associates an integer number starting from zero to each element in a list. This is helpful in loops where an index variable is required.

fruits = ['apple','banana','orange']
for i, fruit in enumerate(fruits):
print i, fruit

Merging two lists[edit]

The zip() function associates the elements of two lists to a single list of tuple. Excess elements are ignored.

fruits = ['apple','banana','orange']
prices = [0.55, 0.75, 0.80, 1.23]

for fruit,price in zip(fruits,prices):
print fruit, price