vault backup: 2024-02-03 13:30:25

Affected files:
content/notes/general/python-notes.md

content/notes/general/python-notes.md

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+---
+title:  "Python Notes"
+tags:
+created: 2024-02-03
+---
+# Python Notes
+---
+- Dynamically typed (types are determined at run time).
+
+## Multiple assignment:
+```python
+n, m = 0, "abc"
+```
+
+- None is `null`.
+
+- Multi-line conditions, we need the parenthesis as we have things in different lines:
+```python
+n, m = 1, 2
+if ((n > 2 and
+    n != m) or n == m):
+    n += 1
+```
+
+## We can do conditionals like this:
+```python
+n = 1
+if n > 2:
+    n -= 1
+elif n == 2:
+    n *= 2
+else:
+    n += 2
+```
+
+## Loops
+- While loop:
+```python
+n = 0
+while n < 5:
+    print(n)
+    n += 1
+```
+
+- For loop, `i` is incremented automatically (we get 0 to 4):
+```python
+for i in range(5):
+    print(i)
+```
+
+```python
+# start at 2 and not include 6
+for i in range(2, 6):
+    print(i)
+
+# the opposite (going backwards)
+for i in rage(5, 1, -1):
+    print(i)
+```
+
+## Math
+```python
+import math
+
+# 2 to the power of 3
+print(math.pow(2, 3))
+print(math.sqrt(2))
+print(math.floor(3/2)) # 1
+print(math.ceil(3/2)) # 2
+
+# double slash rounds down
+print(5//2) # 2
+print(5/2) # 2.5
+```
+
+## Arrays
+- Also called lists.
+
+```python
+arr = [1, 2, 3]
+print(arr)
+
+# can use as stack
+arr.append(4)
+arr.append(5)
+print(arr) # [1, 2, 3, 4, 5]
+
+arr.pop()
+print(arr) # [1, 2, 3, 4]
+
+# location and value
+arr.insert(1, 7)
+print(arr) #  [1, 7, 2, 3, 4]
+
+arr[0] = 0
+arr[3] = 0
+print(arr) # [0, 7, 2, 0, 4]
+
+# initialise arr of size n with default value of 1
+n = 5
+arr = [1] * n
+print(arr) # [1. 1. 1. 1. 1]
+print(len(arr)) # 5
+
+arr = [1, 2, 3]
+print(arr[-1]) # last value (3)
+print(arr[-2]) # 2
+
+# sublists (slicing)
+arr = [1, 2, 3, 4]
+print(arr[1:3]) # 3 not included, so = [2, 3]
+
+# unpacking
+a, b, c = [1, 2, 3]
+print(a, b, c) # 1 2 3
+
+# loop through arrays
+
+```