Merge pull request #47 from surister/new_python_answers
New python answers
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README.md
110
README.md
@ -2250,12 +2250,57 @@ def return_sum():
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<details>
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<summary>How do you swap values between two variables?</summary><br><b>
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```
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x, y = y, x
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```
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</b></details>
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<details>
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<summary>How to check if all the elements in a given lists are unique? so [1, 2, 3] is unique but [1, 1, 2, 3] is not unique but we 1 twice</summary><br><b>
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</b></details>
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<summary>How to check if all the elements in a given lists are unique? so [1, 2, 3] is unique but [1, 1, 2, 3] is not unique because 1 exists twice</summary><br><b>
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</b>
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There are many ways of solving this problem:<br>
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<code># Note: :list and -> bool are just python typings, they are not needed for the correct execution of the algorithm. </code>
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Taking advantage of sets and len:
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```
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def is_unique(l:list) -> bool:
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return len(set(l)) == len(l)
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```
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This one is can be seen used in other programming languages.
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```
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def is_unique2(l:list) -> bool:
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seen = []
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for i in l:
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if i in seen:
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return False
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seen.append(i)
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return True
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```
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Here we just count and make sure every element is just repeated once.
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```
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def is_unique3(l:list) -> bool:
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for i in l:
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if l.count(i) > 1:
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return False
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return True
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```
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This one might look more convulated but hey, one liners.
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```
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def is_unique4(l:list) -> bool:
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return all(map(lambda x: l.count(x) < 2, l))
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```
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</details>
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<details>
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<summary>What _ is used for in Python?</summary><br><b>
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@ -2404,7 +2449,66 @@ def reverse_string(string):
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<details>
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<summary>What empty <code>return</code> returns?</summary><br><b>
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</b></details>
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</b>
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Short answer is: It returns a None object.
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We could go a bit deeper and explain the difference between
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```
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def a ():
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return
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>>> None
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```
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And
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```
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def a ():
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pass
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>>> None
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```
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Or we could be asked this as a following question, since they both give the same result.
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We could use the dis module to see what's going on:
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```
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2 0 LOAD_CONST 0 (<code object a at 0x0000029C4D3C2DB0, file "<dis>", line 2>)
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2 LOAD_CONST 1 ('a')
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4 MAKE_FUNCTION 0
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6 STORE_NAME 0 (a)
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5 8 LOAD_CONST 2 (<code object b at 0x0000029C4D3C2ED0, file "<dis>", line 5>)
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10 LOAD_CONST 3 ('b')
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12 MAKE_FUNCTION 0
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14 STORE_NAME 1 (b)
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16 LOAD_CONST 4 (None)
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18 RETURN_VALUE
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Disassembly of <code object a at 0x0000029C4D3C2DB0, file "<dis>", line 2>:
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3 0 LOAD_CONST 0 (None)
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2 RETURN_VALUE
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Disassembly of <code object b at 0x0000029C4D3C2ED0, file "<dis>", line 5>:
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6 0 LOAD_CONST 0 (None)
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2 RETURN_VALUE
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```
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An empty <code> return</code> is exactly the same as <code>return None</code> and functions without any explicit return
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will always return None regardless of the operations, therefore
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```
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def sum(a, b):
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global c
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c = a + b
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>>> None
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```
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</details>
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##### Time Complexity
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