Answer to Question #126617 in Python for Ola Unwana

Question

Give at least three examples that show different features of string slices. Describe the feature illustrated by each example. Invent your own examples. Do not copy them for the textbook or any other source.

Answer 1

print('Example 1: Substrings and every i-th character')

string = 'Describe the feature illustrated by each example.'

strA = string[0:9]

strB = string[9::2]

strC = string[10::2]

listD = [x + y for x, y in zip(strB, strC)]

string2 = strA + ''.join(listD)

print(string2)

assert string2 == string

print('')




print('Example 2: Ranges and slices and slice objects')

# docs.python.org/3/library/functions.html#slice

nums = list(range(1,10))

nums2 = nums[:-1:2] + [nums[-1]] + nums[1::2] + nums[50:100:3]

nums3 = list(range(1,10,2)) + list(range(2,10,2))

print(nums2)

print(nums3)

assert nums2 == nums3

string = 'Describe the feature illustrated by each example.'

string2 = string[:-1:2] + string[-1] + string[1::2] + string[50:100:3]

lstA = [string[i] for i in range(0,len(string),2)]

# lstB = [string[i] for i in range(1,len(string),2)]  # what a mess

# lstB = string[slice(1,len(string),2)]  # string, not a list :)

lstB = list(string)[slice(1,len(string),2)]

lstC = [string[i] for i in range(50,100,3) if i in range(len(string))]

string3 = ''.join(lstA) + ''.join(lstB) + ''.join(lstC)

print(string2)

print(string3)

assert string2 == string3

print('')




print('Example 3: Copying and reversing')

string = 'Describe the feature illustrated by each example.'

string2 = string[:]

try: string2[-1] = '!'

except TypeError as e: print(e)

string3 = string

try: string3[-1] = '!'

except TypeError as e: print(e)

string = ''.join(reversed(string))  # it's slower then slicing

string2 = string2[::-1]

print(string)

print(string2)

print(string3)

assert string2 == string

print('')