20170628.md

內建函數 item()

thitems()function doesn't return key/value pairs in any specific order.

my_dict = {
'Name':'Jiayi',
'Age':20,
'height':155
}
print my_dict.items()

[( 'Age', 20), ( 'Name', 'Jiayi' ), ( 'height' , 155) ]

---

Key() and Values()

Thekeys()function returns an array of the dictionary's keys, and

Thevalues()function returns an array of the dictionary's values.

my_dict = {
'Name':'Jiayi',
'Age':20,
'height':155
}

print my_dict.keys()
print my_dict.values()

['Name', 'Age', 'height' ]

['Jiayi', 20, 155 ]

---

You can useinveryintuitively, like so:

my_dict = {
'Name':'Jiayi',
'Age':20,
'height':155
}

for key in my_dict:
print key, my_dict[key]

Age 20

Name Jiayi

height 155

for letter in 'JIAYI':
    print letter

J

I

A

Y

I

---

Building Lists

evens_to_50 = [i for i in range(51) if i % 2 == 0]
print evens_to_50

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50]

even_squares = [y**2 for y in range(1,11) if (y**2) % 2 == 0]
print y

[4, 16, 36, 64, 100]

List Slicing Syntax

[start:end:stride]

Wherestartdescribes where the slice starts (inclusive),endis where it ends (exclusive), andstridedescribes the space between items in the sliced list. For example, a stride of2would select every other item from the original list to place in the sliced list.

l = [i ** 2 for i in range(1, 11)]
# Should be [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
print l[2:9:2]

[9, 25, 49, 81]

Omitting Indices

The default starting index is0

The default ending index is the end of the list

The default stride is1

to_five = ['A', 'B', 'C','D','E']
print to_five[3:]
# prints ['D', 'E'] 
print to_five[:2]
# prints ['A', 'B']
print to_five[::2]
# print ['A', 'C', 'E']

my_list = range(1, 11) # List of numbers 1 - 10
print my_list[0::]
print my_list[::2]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

[1, 3, 5, 7, 9]

Reversing a List

my_list = range(1, 11)
backwards =  my_list[::-1]
print backwards

[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]