python-study-notes

reference to do basic operations on iterable objects

get substring	add item	remove item	filter list	map list
split by delimiter	join with delimiter	reverse list	sort list	get max
get min	is item in list	is instance of type	get index of item in list	get indices of item in list
iterate by index	get column in 2d matrix	uppercase string	lowercase string	get unique list items

---

get substring

letters = "abcdef"
r = letters[0]
print(r)

>> "a"

letters = "abcdef"
r = letters[:-1]
print(r)

>> "abcde"

letters = "abcdef"
r = letters[1:]
print(r)

>> "bcdef"

letters = "abcdef"
r = letters[1:-1]
print(r)

>> "bcde"

---

add item

items = [1,2,3,4,5]
items.append(6)
print(items)

>> [1, 2, 3, 4, 5, 6]

items = [1,2,3,4,5]
items.insert(2, 'r')
print(items)

>> [1, 2, 'r', 3, 4, 5]

---

remove item

items = [1,2,3,4,5]
del items[0:2]
print(items)

>> [3, 4, 5]

items = [1,2,3,4,5]
items.pop(2)
print(items)

>> [1, 2, 4, 5]

---

filter list

items = [1,2,3,4,5,6,7,8]
r = [i for i in items if i % 2 == 0]
print(r)

>> [2, 4, 6, 8]

items = [1,2,3,4,5,6,7,8]
r = list(filter(lambda i: i % 2 == 0, items))
print(r)

>> [2, 4, 6, 8]

---

map list

items = [1,2,3,4,5]
r = [i * 2 for i in items]
print(r)

>> [2, 4, 6, 8, 10]

items = [1,2,3,4,5]
r = list(map(lambda i: i * 2, items))
print(r)

>> [2, 4, 6, 8, 10]

---

split by delimiter

letters = 'a b c d e f'
r = letters.split(' ')
print(r)

>> ['a', 'b', 'c', 'd', 'e', 'f']

---

join with delimiter

items = ['a','b','c','d','e']
r = " ".join(items)
print(r)

>> "a b c d e"

---

reverse list

items = [1,2,3,4,5]
r = items[::-1]
print(r)

>> [5, 4, 3, 2, 1]

items = [1,2,3,4,5]
items.reverse()
print(items)

>> [5, 4, 3, 2, 1]

---

sort list

items = [2,4,6,1,2,3]
r = sorted(items)
print(r)

>> [1, 2, 2, 3, 4, 6]

items = [2,4,6,1,2,3]
r = sorted(items, reverse=True)
print(r)

>> [6, 4, 3, 2, 2, 1]

---

get max

items = [1,2,3,6,5,4]
r = max(items)
print(r)

>> 6

---

get min

items = [6,5,4,1,2,3]
r = min(items)
print(r)

>> 1

---

is item in list

items = ['a','b','c','d','e']
print(True) if ('d' in items) else print(False)

>> True

---

is instance of type

isinstance([1,2,3], list)

>> True

isinstance({'a': 1, 'b': 2}, dict)

>> True

---

get index of item in list

items = ['a','b','c','d','e']
r = items.index('c')
print(r)

>> 2

---

get indices of item in list

items = [1,2,3,2,4,6,3,6,9]
r = [i for i in range(len(items)) if items[i] == 3]
print(r)

>> [2, 6]

---

iterate by index

items = ['a','b','c','d','e']
for i in range(len(items)):
  print(i, end=' ')

>> 0 1 2 3 4

---

get column in 2d matrix

items = [
  [1,2],
  [3,4],
  [5,6],
  ]
r = [i[0] for i in items]
print(r)

>> [1, 3, 5]

---

uppercase string

letters = "abcde"
r = letters.upper()
print(r)

>> 'ABCDE'

---

lowercase string

letters = "ABCDE"
r = letters.lower()
print(r)

>> 'abcde'

---

get unique list items

items = [1,2,2,3,3,3]
r = []
for i in items: i not in r and r.append(i)
print(r)

>> [1, 2, 3]