Subversion Repositories Boeken.quickpython

08.3 For loop

x = [1.0, 2.0, 3.0]
for n in x:
    print(1 / n)

08.3.1 range function

x = [1, 3, -7, 4, 9, -5, 4]
for i in range(len(x)):
    if x[i] < 0:
        print("Found a negative number at index ", i)

>>> list(range(3, 7))           #1
[3, 4, 5, 6]
>>> list(range(2, 10))          #1 
[2, 3, 4, 5, 6, 7, 8, 9]        
>>> list(range(5, 3))
[]


>>> list(range(0, 10, 2))
[0, 2, 4, 6, 8]
>>> list(range(5, 0, -1))
[5, 4, 3, 2, 1]


08.3.3 The for loop and tuple unpacking

somelist = [(1, 2), (3, 7), (9, 5)]
result = 0
for t in somelist:
    result = result + (t[0] * t[1])

somelist = [(1, 2), (3, 7), (9, 5)]
result = 0

for x, y in somelist:
    result = result + (x * y)

08.3.4 enumerate function

x = [1, 3, -7, 4, 9, -5, 4]
for i, n in enumerate(x):                               #1
    if n < 0:                                           #2
        print("Found a negative number at index ", i)   #3

08.3.5 zip function 

>>> x = [1, 2, 3, 4]
>>> y = ['a', 'b', 'c']           #A 
>>> z = zip(x, y)
>>> list(z)
[(1, 'a'), (2, 'b'), (3, 'c')]    #B


08.4 List and dictionary comprehensions

>>> x = [1, 2, 3, 4]
>>> x_squared = []
>>> for item in x:
...     x_squared.append(item * item)
... 
>>> x_squared
[1, 4, 9, 16]


>>> x = [1, 2, 3, 4]
>>> x_squared = [item * item for item in x]
>>> x_squared
[1, 4, 9, 16]


>>> x = [1, 2, 3, 4]
>>> x_squared = [item * item for item in x if item > 2]

>>> x_squared
[9, 16]


>>> x = [1, 2, 3, 4]
>>> x_squared_dict = {item: item * item for item in x}
>>> x_squared_dict
{1: 1, 2: 4, 3: 9, 4: 16}

08.4.1 Generator Expressions

>>> x = [1, 2, 3, 4]
>>> x_squared = (item * item for item in x)
>>> x_squared
<generator object <genexpr> at 0x102176708>
>>> for square in x_squared:
...     print(square,)
...
1 4 9 16

08.5 Statements, blocks, and indentation 

>>> x = 1; y = 0; z = 0
>>> if x > 0: y = 1; z = 10
... else: y = -1
... 
>>> print(x, y, z)
1 1 10


>>>
>>>   x = 1
File "<stdin>", line 1
    x = 1
    ^
   IndentationError: unexpected indent
>>>


>>> x = 1
>>> if x == 1: 
...    y = 2
...    if v > 0:
...        z = 2
...        v = 0
...
>>> x = 2


>>> x = 1
>>> if x == 1:
           y = 2
        z = 2
File "<stdin>", line 3
       z = 2
       ^
    IndentationError: unindent does not match any outer indentation level


>>> print('string1', 'string2', 'string3' \
...    , 'string4', 'string5')
string1 string2 string3 string4 string5
>>> x = 100 + 200 + 300 \
...    + 400 + 500
>>> x
1500
>>> v = [100, 300, 500, 700, 900,
...    1100, 1300]
>>> v
[100, 300, 500, 700, 900, 1100, 1300]
>>> max(1000, 300, 500,
...        800, 1200)
1200
>>> x = (100 + 200 + 300
...          + 400 + 500)
>>> x
1500


>>> "strings separated by whitespace "    \
...    """are automatically"""  ' concatenated'
'strings separated by whitespace are automatically concatenated'
>>> x = 1
>>> if x > 0:
...        string1 = "this string broken by a backslash will end up \
...                with the indentation tabs in it"
...
>>> string1
'this string broken by a backslash will end up \t\t\twith
     the indentation tabs in it'
>>> if x > 0:
...        string1 = "this can be easily avoided by splitting the " \ 
...            "string in this way"
...
>>> string1
'this can be easily avoided by splitting the string in this way'

08.6.2 Comparison and Boolean operators

>>> [2] and [3, 4]
[3, 4]
>>> [] and 5
[]
>>> [2] or [3, 4]
[2]
>>> [] or 5
5
>>> 


>>> x = [0]
>>> y = [x, 1]
>>> x is y[0]            #A
True
>>> x = [0]              #B
>>> x is y[0]
False
>>> x == y[0]
True