python快速入门【一】-----基础语法

# This is a one line comment
print('Hello World!')

Hello World!

# Strings can be enclosed by ',", or """
print("Hello World!")

Hello World!

# \ is used as a escape character. 
# There are many special escape sequences
# Notable are: \t (tab)
#             \n (new line)

print("The \n makes a new line")

The 
 makes a new line

print("The \t is a tab")

The 	 is a tab

print('I\'m going to the movies')

I'm going to the movies

# Using \ to not accidently close the string by having a closing "
print("This is a string enclosed by \"\" not '' ")

This is a string enclosed by "" not '' 

# Creating a variable
# Variables are used to store information to be referenced 
# and manipulated in a computer program.

firstVariable = 'Hello World'
print(firstVariable)

Hello World

# go over ? mark after if you are not sure what method does. 
print(firstVariable.lower())
print(firstVariable.upper())
print(firstVariable.title())

hello world
HELLO WORLD
Hello World

# To look up what each method does
firstVariable.lower?

# Can also use help
help(firstVariable.lower)

Help on built-in function lower:

lower(...)
    S.lower() -> string
    
    Return a copy of the string S converted to lowercase.

help

firstVariable.split(' ')

['Hello', 'World']

a=firstVariable.split(' ')
a

['Hello', 'World']

' '.join(a)

'Hello World'

print("0" + "1")

01

"0" * 3

'000'

# You can add strings together. 
"Fizz" + "Buzz"

'FizzBuzz'

# Addition, add two int together
1+1

2

# if one of the operands is a float, the result is a float.
130-2.0  

128.0

130-2

128

# integer division
130/2    

65.0

130.0/2

65.0

# Multiplication
2*3

6

# Exponentiation ** 
# This operator raises the number to its left to the power of the number to its right 
2**3

8

# Modulo
# Returns the remainder of the division of the number to the left by the 
# number on its right. 
9%3

0

# Notice you have to indent after you start a if statement. 
num = 3
if num == 3: 
    print(num)

3

# Nothing is outputted because num > 10 is FALSE
num = 3
if num > 10:
    print(num)

num = 3
if num % 3 == 0:
    print("Fizz")

Fizz

num = 10
if num % 5 == 0:
    print("Buzz")

Buzz

if True:
    print("This was True")

This was True

if False: 
    print("Nothing printed")

num = 4
num > 0 and num  < 15

True

# both the conditions are true, so the num will be printed out
if num > 0 and num  < 15:
    print(num)

4

# num > 0 is True, num > 15 is False
# Since the first condition is True, it is True
num = 4
num > 0 or num  > 15

True

if num > 0 or num  > 15:
    print(num)

4

# or will only evaluate to False if both are False
if False or False:
    print('Nothing will print out')

num = 10
not num < 20 

False

num = 1
if num > 3 :
    print("Hi")

"""We will execute what is inside the else statement
because num is not greater than 3
"""
num = 1
if num > 3 :
    print("Hi")
else: 
    print("number is not greater than 3")

number is not greater than 3

"""We will execute what is inside the if statement because num > 4"""
num = 4
if num > 3 :
    print("Hi")
else: 
    print("number is not greater than 3")

Hi

num = 3
if num % 2 == 0:
    print("Your integer is even")
else: 
    print("Your integer is odd")

Your integer is odd

num = 21
if num > 50:
    print('num is larger than 50')
elif num == 21:
    print('num = 21')
else:
    print('Catchall condition')

num = 21

my_num = 5
if my_num % 2 == 0:
    print("Your number is even")
elif my_num % 2 != 0:
    print("Your number is odd")
else: 
    print("Are you sure your number is an integer?")

Your number is odd

# You can have mulitple elif statements. 
# Remember only the first True statement has its block of code executed. 

dice_value = 1
if dice_value == 1:
    print('You rolled a {}. Great job!'.format(dice_value))
elif dice_value == 2:
    print('You rolled a {}. Great job!'.format(dice_value))
elif dice_value == 3:
    print('You rolled a {}. Great job!'.format(dice_value))
elif dice_value == 4:
    print('You rolled a {}. Great job!'.format(dice_value))
elif dice_value == 5:
    print('You rolled a {}. Great job!'.format(dice_value))
elif dice_value == 6:
    print('You rolled a {}. Great job!'.format(dice_value))
else:
    print('None of the conditions above (if elif) were evaluated as True')

You rolled a 1. Great job!

# Solution 1
num = 10

if num % 3 == 0 and num % 5 == 0:
    print('FizzBuzz')
elif num % 3 == 0:
    print('Fizz')
elif num % 5 == 0:
    print('Buzz')
else:
    print(str(num))

Buzz

# Solution 2
num = 15

"""Notice how difficult this solution is relative to Solution 1"""

string = ""
if num % 3 == 0:
    string = string + "Fizz"
if num % 5 == 0:
    string = string + "Buzz"
if num % 5 != 0 and num % 3 != 0:
    string = string + str(num)
print(string)

FizzBuzz

# Defining a list
z = [3, 7, 4, 2]

# The first element of a list is at index 0
z[0]

3

z[2]

4

# Access Last Element of List 
z[-2]

4

# first index is inclusive (before the :) and last (after the :) is not. 
# not including index 2
z[0:2]

[3, 7]

# everything up to index 3
z[:3]

[3, 7, 4]

# index 1 to end of list
z[1:]

[7, 4, 2]

print(min(z), max(z), len(z), sum(z))

2 7 4 16

random_list = [4, 1, 5, 4, 10, 4]
random_list.count(4)

3

random_list.index(4)

0

# you can specify where you start your search
random_list.index(4, 3)

3

# random_list.index(value, [start, stop])
random_list.index(4, 5, 6)

5

x = [3, 7, 2, 11, 8, 10, 4]
y = ['Steve', 'Rachel', 'Michael', 'Adam', 'Monica', 'Jessica', 'Lester']

# Sorting and Altering original list
# low to high
x.sort()
print(x)

[2, 3, 4, 7, 8, 10, 11]

# Sorting and Altering original list
# high to low
x.sort(reverse = True)
print(x)

[11, 10, 8, 7, 4, 3, 2]

# Sorting and Altering original list
# A-Z
y.sort()
print(y)

['Adam', 'Jessica', 'Lester', 'Michael', 'Monica', 'Rachel', 'Steve']

# Sorting and Altering original list
# Z-A
y.sort(reverse = True)
print(y)

['Steve', 'Rachel', 'Monica', 'Michael', 'Lester', 'Jessica', 'Adam']

# sorting list WITHOUT altering original list 
new_list = sorted(y)
new_list

['Adam', 'Jessica', 'Lester', 'Michael', 'Monica', 'Rachel', 'Steve']

# notice y is unchanged
y

['Steve', 'Rachel', 'Monica', 'Michael', 'Lester', 'Jessica', 'Adam']

x

[11, 10, 8, 7, 4, 3, 2]

x.append(3)
print(x)

[11, 10, 8, 7, 4, 3, 2, 3]

x.remove(10)
print(x)

[11, 8, 7, 4, 3, 2, 3]

# List before you remove an item
print(x)

[11, 8, 7, 4, 3, 2, 3]

# Remove item at the index
# this function will also return the item you removed from the list
# Default is the last index
x.pop(3)

4

print(x)

[11, 8, 7, 3, 2, 3]

x.extend([4, 5])

x

[11, 8, 7, 3, 2, 3, 4, 5]

# lists can be diverse, each element in the list can be of a different type.
# lists are really list of pointers, and these pointers can 
# point to anything.

# Concatenating Lists
print('x+y=',x+y)

x+y= [11, 8, 7, 3, 2, 3, 4, 5, 'Steve', 'Rachel', 'Monica', 'Michael', 'Lester', 'Jessica', 'Adam']

x

[11, 8, 7, 3, 2, 3, 4, 5]

x.insert(4, [4, 5])

x

[11, 8, 7, 3, [4, 5], 2, 3, 4, 5]