Python basic grammar (miscellaneous) Memo (2)

2.7 base. (1) is here.

Conditional statement / control structure

Authenticity

Python determines whether all objects will be True or False when treated as a bool value.

>>> a = 0
>>> print a == 0
True
>>> print a == True
False
>>> print a == False
True

>>> a = 1
>>> print a == True
True
>>> print a == False
False

if Add a colon to the end of the conditional expression.

>>> a = 0
>>> if a:
    print 'TRUE'
else:
    print 'FALSE'
    
FALSE

#Inversion by not
>>> if not a:
    print 'TRUE'
else:
    print 'FALSE'
    
TRUE

#Type determination with isinstance
>>> if isinstance(a, int):
    print 'Integer'
    
Integer

#Comparison operators are standard
>>> if a <= 3
    print 'Less than 3'
    
Less than 3

#In or not in to indicate whether it is included in a list or tuple element
>>> list = [0,1,2,3,4]
>>> if 3 in list
    print 'found'
    
found

#Add condition with elif
a = raw_input('input number >')
a = int(a)
if a < 5:
    print 'less than 5'
elif a < 10:
    print 'less than 10'
else:
    print 'greater than or equal to 10'

Logical operator

• x and y
• x or y
• not x

>>> a = 5
>>> if a > 3 and a < 5:
   print 'True'
else
   print 'False'
   
False

while

>>> while a < 3:
...     print('sushi')
...     a += 1
...
sushi
sushi
sushi

for..in.. Use as an Iterator for lists and tuples.

>>> sushi = ['maguro', 'hamachi', 'engawa']
>>> for s in sushi:
...     print s
...
maguro
hamachi
engawa

range The built-in function range () produces a list with arithmetic progressions as elements.

>>> for i in range(3):
...     print 'hoge'
...
hoge
hoge
hoge

• range(x)
  Create a list from 0 to x
• range(x, y)
  Create a list from x to y
• range(x, y, z)
  Create a list for each z in the range x to y-1

Exception handling

try:
Processing that may cause an exception
except exception name:
Error handling
else:
What to do when an exception does not occur
finally:
Processing that must pass

a = ['a', 'b', 'c']
number = int(raw_input('input a number > '))

try:
    b = a[number]
except IndexError:
    print 'index error!(' + str(number) + ')'
else:
    print b
finally:
    print 'end of program'
    

Sample: Computational Problem Challenge

#Import module
import time
import random

num_of_times = 5
game_time = 25
num_of_range = 100
start_time = time.time() #Current time

for i in range(num_of_times):
	#Create double-digit random addition
    a = random.randint(1, num_of_range)
    b = random.randint(1, num_of_range)
    c = a + b
    ans = input(str(a) + '+' + str(b) + '= ' ) #Substitute keyboard input for ans

    if ans != c:
        print 'wrong answer'
        print 'answer is ' + str(c)
        break

    elif time.time() - start_time > game_time:
        print 'timeout'
        break

    else:
        print 'Bingo!'

else:
    #Pass here only when exiting the for loop (all correct answers)
    print 'Complete!'
    
print 'end of program'