Four copies of the last two characters

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Python Practice › String Programs › Program 3

Four copies of the last two characters

EasyString Programs · 3 of 106

Write a Python program to make a string of 4 copies of the last two characters of a string (length must be at least 2).

Input
"Python"
Output
onononon

Approach

  1. Slice the last two characters and repeat them with * 4.

Solution

Python
text = "Python"if len(text) >= 2:    print(text[-2:] * 4)else:    print("String must have at least 2 characters")
Output
onononon

Line by line

Line 3

text[-2:] is “on”; multiplying a string repeats it.

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Length of the longest string in a list

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Python Practice › String Programs › Program 2

Length of the longest string in a list

EasyString Programs · 2 of 106

Write a Python program that returns the length of the longest string in a list.

Input
["python", "is", "readable", "fun"]
Output
8 | 8 | readable

Approach

  1. Compare lengths in a loop, or use max() with len.

Solution

Python
words = ["python", "is", "readable", "fun"]longest = 0for w in words:    if len(w) > longest:        longest = len(w)print(longest, "|", max(len(w) for w in words), "|", max(words, key=len))
Output
8 | 8 | readable

Line by line

Lines 3-5

Keep the biggest length seen so far.

Line 6

max(len(w) for w in words) does the same in one line; max(words, key=len) returns the word itself.

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First and last 2 characters

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Python Practice › String Programs › Program 1

First and last 2 characters

EasyString Programs · 1 of 106

Write a Python program to build a string from the first 2 and the last 2 characters of a string. If the string is shorter than 2 characters, return an empty string.

Input
"Sqatools", "Py", "S"
Output
'Sqatools' -> 'Sqls'
'Py' -> 'PyPy'
'S' -> ''

Approach

  1. Check the length first; then join two slices.

Solution

Python
def ends(text):    if len(text) < 2:        return ""    return text[:2] + text[-2:] for t in ["Sqatools", "Py", "S"]:    print(repr(t), "->", repr(ends(t)))
Output
'Sqatools' -> 'Sqls'
'Py' -> 'PyPy'
'S' -> ''

Line by line

Lines 2-3

Strings shorter than 2 characters return an empty string, as the task asks.

Line 4

text[:2] is the first two characters and text[-2:] the last two.

Note

For “Py” the two slices overlap, so the result is “PyPy”.

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Round every number and sum

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Python Practice › List Programs › Program 99

Round every number and sum

EasyList Programs · 99 of 100

Write a Python program to round every number in a list and print the sum of the rounded numbers multiplied by the list length.

Input
[22.4, 4.0, -16.22, -9.1, 11.0, -12.22, 14.2, -5.2, 17.5]
Output
[22, 4, -16, -9, 11, -12, 14, -5, 18]
243

Approach

  1. Round each value with round(), add them, multiply by the length.

Solution

Python
numbers = [22.4, 4.0, -16.22, -9.1, 11.0, -12.22, 14.2, -5.2, 17.5]rounded = [round(n) for n in numbers]print(rounded)print(sum(rounded) * len(numbers))
Output
[22, 4, -16, -9, 11, -12, 14, -5, 18]
243

Line by line

Line 2

round(17.5) is 18 and round(-12.22) is -12; ties go to the even number.

Note

The sum of the rounded numbers is 27; multiplied by the 9 items it is 243.

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Decode a run-length encoded list

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Python Practice › List Programs › Program 98

Decode a run-length encoded list

MediumList Programs · 98 of 100

Write a Python program to decode a run-length encoded list, where [n, x] means x repeated n times.

Input
[[2, 1], 2, 3, [2, 4], 5, 1]
Output
[1, 1, 2, 3, 4, 4, 5, 1]

Approach

  1. Expand [n, x] pairs; copy plain items.

Solution

Python
encoded = [[2, 1], 2, 3, [2, 4], 5, 1]decoded = []for item in encoded:    if isinstance(item, list):        count, value = item        decoded.extend([value] * count)    else:        decoded.append(item)print(decoded)
Output
[1, 1, 2, 3, 4, 4, 5, 1]

Line by line

Lines 5-6

[value] * count repeats the value.

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Remove repeated dictionaries

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Python Practice › List Programs › Program 97

Remove repeated dictionaries

EasyList Programs · 97 of 100

Write a Python program to remove repeated dictionaries from a list.

Input
[{"Hello": 5}, {"student": 7}, {"are": 3}, {"learning": 8}, {"Hello": 5}, {"Language": 8}, {"are": 3}]
Output
[{'Hello': 5}, {'student': 7}, {'are': 3}, {'learning': 8}, {'Language': 8}]

Approach

  1. Use a set of each dict’s items (as a frozenset) to remember what was seen.

Solution

Python
data = [{"Hello": 5}, {"student": 7}, {"are": 3}, {"learning": 8}, {"Hello": 5}, {"Language": 8}, {"are": 3}]seen = set()result = []for d in data:    key = frozenset(d.items())    if key not in seen:        seen.add(key)        result.append(d)print(result)
Output
[{'Hello': 5}, {'student': 7}, {'are': 3}, {'learning': 8}, {'Language': 8}]

Line by line

Line 4

frozenset(d.items()) is a hashable fingerprint of the dict, so the check is fast even for long lists.

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Word lengths as a dictionary

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Python Practice › List Programs › Program 96

Word lengths as a dictionary

EasyList Programs · 96 of 100

Write a Python program to build a dictionary of each word and its length.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Language"]
Output
{'Hello': 5, 'student': 7, 'are': 3, 'learning': 8, 'Python': 6, 'Its': 3, 'Language': 8}

Approach

  1. A dict comprehension.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Language"]print({w: len(w) for w in words})
Output
{'Hello': 5, 'student': 7, 'are': 3, 'learning': 8, 'Python': 6, 'Its': 3, 'Language': 8}

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Remove the 2nd character of each word

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Python Practice › List Programs › Program 95

Remove the 2nd character of each word

EasyList Programs · 95 of 100

Write a Python program to remove the 2nd character of each word.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]
Output
['Hllo', 'sudent', 'ae', 'larning', 'Pthon', 'Is', 'Pthon', 'Lnguage']

Approach

  1. Join the slices before and after index 1.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]print([w[0] + w[2:] for w in words])
Output
['Hllo', 'sudent', 'ae', 'larning', 'Pthon', 'Is', 'Pthon', 'Lnguage']

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Capitalise the 3rd character of each word

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Python Practice › List Programs › Program 94

Capitalise the 3rd character of each word

EasyList Programs · 94 of 100

Write a Python program to make the 3rd character of each word uppercase.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]
Output
['HeLlo', 'stUdent', 'arE', 'leArning', 'PyThon', 'ItS', 'PyThon', 'LaNguage']

Approach

  1. Index 2 is the 3rd character; rebuild the word around it.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]print([w[:2] + w[2].upper() + w[3:] if len(w) > 2 else w for w in words])
Output
['HeLlo', 'stUdent', 'arE', 'leArning', 'PyThon', 'ItS', 'PyThon', 'LaNguage']
Note

The original sample changed the 4th character (“HelLo”). The 3rd character is index 2, which gives “HeLlo”.

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Replace a word in a list

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Python Practice › List Programs › Program 93

Replace a word in a list

EasyList Programs · 93 of 100

Write a Python program to replace “Java” with “Python” in a list of words.

Input
["Hello", "student", "are", "learning", "Java", "Its", "Java", "Language"]
Output
['Hello', 'student', 'are', 'learning', 'Python', 'Its', 'Python', 'Language']

Approach

  1. Map each word, replacing the match.

Solution

Python
words = ["Hello", "student", "are", "learning", "Java", "Its", "Java", "Language"]print(["Python" if w == "Java" else w for w in words])
Output
['Hello', 'student', 'are', 'learning', 'Python', 'Its', 'Python', 'Language']

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