Iteration
Python is equipped with strong tools for the repeat of some commands or produce sequence number.
Contents
Range
The function range can be used to produce series of number between two numbers.
range(3,15)
The advance function of range is arange in numpy which can be used to generate a series of number from a number to another number with specific increment:
>>> np.arange(8, 20,1)
array([ 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19])
>>> np.arange(2,1,-0.1)
array([ 2. , 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1])
A specified element can be repeated for specific number.
>>> [2,3]*2
[2, 3, 2, 3]
>>> np.repeat([2, 3],[2,3])
array([2, 2, 3, 3, 3])
>>> np.repeat(["A", "B"],[2,3])
array(['A', 'A', 'B', 'B', 'B'],dtype='<U1')
For
The most useful function for the iteration is for that repeats the specified commands for specified times, run the following codes to see how does it work
>>> for r in range(1,5):
... print(r^3)
...
2
1
0
7
>>> for i in [2,3,1,7]:
... print(i^3)
...
1
0
2
4
>>> score=[10, 15, 7, 20]
>>> for i in (range(0,4)):
... if (score[i]<10):
... print("fail")
... else:
... print("pass")
...
pass
pass
fail
pass
>>> for i in range(0,4):
... if score[i]<10:
... print("fail")
... elif(score[i]>=10&score[i]<14):
... print("middle")
... elif(score[i]>=14&score[i]<17):
... print("good")
... elif(score[i]>=17):
... print("BEST")
...
middle
middle
fail
middle
While
The command while runs iteration until the condition be attained,
>>> x=8
>>> i=0
>>> while(x<12):
... i=i+1
... x=x+x/8
... print(i,x)
...
1 9.0
2 10.125
3 11.390625
4 12.814453125
Inversely, the command of repeat continue until the condition situated inside commands be attained, in the following codes, the loop continues until the condition (x>12) is violated.
>>> x=8
>>> i=0
>>> while True:
... i=i+1
... x=x+x/8
... print(i,x)
... if (x>12):
... break
...
1 9.0
2 10.125
3 11.390625
4 12.814453125
Comprehension structure
Comprehension structure in Python helps to combine several iteration in one line, to practice let write a simple function to select pair of unequal numbers between (1, 100).
combs=[]
for x in range(3):
for y in range(3):
if x!= y:
combs.append((x,y))
The code can be simplify as list comprehension
[(x,y) for x in range(3) for y in range(3) if x!=y]
Comprehension structure can be used for different Python structures, see the following script that generates numbers between (1,10) and put them in different Python structures.
# A generator expression
print ((x for x in range(10)))
# A list comprehension
print ([x for x in range(10)])
# A set comprehension
print ({x for x in range(10)})
# A dictionary comprehension
print ({x: x for x in range(10)})
License
Copyright (c) 2019 Saeid Amiri
