Variables

To assign the value 365 to the variable days, we enter the variable name, add an equals sign (=)

days = 365

days_1 = 365
days_2 = 366

number_of_days = 365
number_of_days = 366

print(365)

number_of_days = 365
print(number_of_days)

输出 ： 365

Data Types

When we assign a value an integer value to a variable, we say that the variable is an instance of the integer class

The two most common numerical types in Python are integer and float

The most common non-numerical type is a string

str_test = "China"
int_test = 123
float_test = 122.5

print(str_test)
print(int_test)
print(float_test)

输出 ：
China
123
122.5

print(type(str_test))
print(type(int_test))
print(type(float_test))

输出 ：
<class 'str'>
<class 'int'>
<class 'float'>

str_eight = str(8)  
#str_eight + 10
print (type(str_eight))
eight = 8
str_eight_two = str(eight)

str_eight = "8"
int_eight = int(str_eight)
int_eight + 10
print (type(int_eight))

输出 ：
<class 'str'>
<class 'int'>

str_test = 'test'
str_to_int = int(str_test)

输出 ：

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-42-175cd8fdcd31> in <module>()
      1 str_test = 'test'
----> 2 str_to_int = int(str_test)

ValueError: invalid literal for int() with base 10: 'test'

Comments

print test

"""
Addition: +
Subtraction: -
Multiplication: *
Division: /
Exponent: **
"""

输出 ： '\nAddition: +\nSubtraction: -\nMultiplication: *\nDivision: /\nExponent: **\n'

china=10
united_states=100
china_plus_10 = china + 10
us_times_100 = united_states * 100
print(china_plus_10)
print(us_times_100)
print (china**2)

输出 ：
20
10000
100

#LIST
months = []
print (type(months))
print (months)
months.append("January")
months.append("February")
print (months)

输出 ：
<class 'list'>
[]
['January', 'February']

months = []
months.append(1)
months.append("January")
months.append(2)
months.append("February")
print (months)

输出 ： [1, 'January', 2, 'February']

temps = ["China", 122.5, "India", 124.0, "United States", 134.1]

countries = []
temperatures = []

countries.append("China")
countries.append("India")
countries.append("United States")

temperatures.append(30.5)
temperatures.append(25.0)
temperatures.append(15.1)

print (countries)
print (temperatures)
china = countries[0]
china_temperature = temperatures[1]
print (china)
print (china_temperature)

输出 ：
['China', 'India', 'United States']
[30.5, 25.0, 15.1]
China
25.0

int_months = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
length = len(int_months) # Contains the integer value 12.
print (length)

输出 ： 12

int_months = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
index = len(int_months) - 1
last_value = int_months[index] # Contains the value at index 11.
print (last_value)
print (int_months[-1])

输出 ：
12
12

#Slicing 
months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul"]
# Values at index 2, 3, but not 4.
two_four = months[2:4]
print (two_four)

输出 ： ['Mar', 'Apr']

three_six = months[3:]
print (three_six)

输出 ： ['Apr', 'May', 'Jun', 'Jul']

#Files
#To open a file in Python, we use the open() function
f = open("test.txt", "r")

g = f.read()
print(g)

f.close()

输出 ：
hello python
tangyudi 123
ML 456
DL 789
data 234

f = open("test_write.txt", "w")

f.write('123456')
f.write('\n')
f.write('234567')

f.close()

# We can split a string into a list.
sample = "john,plastic,joe"
split_list = sample.split(",")
print(split_list)

# Here's another example.
string_two = "How much wood\ncan a woodchuck chuck\nif a woodchuck\ncould chuck wood?"
split_string_two = string_two.split('\n')
print(split_string_two)

# Code from previous cells
f = open('test.txt', 'r')
data = f.read()
rows = data.split('\n')
print(rows[0:3])

输出 ：
['john', 'plastic', 'joe']
['How much wood', 'can a woodchuck chuck', 'if a woodchuck', 'could chuck wood?']
['hello python', 'tangyudi 123', 'ML 456']

#loop
cities = ["Austin", "Dallas", "Houston"]
for city in cities:        
    print(city)
print ('123')

输出 ：
Austin
Dallas
Houston
123

i = 0
while i < 3:
    i += 1
    print (i)

输出 ：
1
2
3

for i in range(15):
    print (i)

输出 ：
0
1
2
3
4
5
6
7
8
9

cities = [["Austin", "Dallas", "Houston"],['Haerbin','Shanghai','Beijing']]
#print (cities)
for city in cities:
    print(city)
    

for i in cities:
    for j in i:
        print (j)

输出 ：
['Austin', 'Dallas', 'Houston']
['Haerbin', 'Shanghai', 'Beijing']
Austin
Dallas
Houston
Haerbin
Shanghai
Beijing

#Booleans

cat = True
dog = False
print(type(cat))

输出 ： <class 'bool'>

print(8 == 8) # True
print(8 != 8) # False
print(8 == 10) # False
print(8 != 10) # True

print ("abc" == "abc")
print (["January", "February"] == ["January", "February"])
print (5.0 == 5.0)

输出 ：
True
False
False
True
True
True
True

rates = [10, 15, 20]

print (rates[0] > rates[1]) # False
print (rates[0] >= rates[0]) # True

输出 ：
False
True

#If Statements
sample_rate = 700
greater = (sample_rate > 5)
if 0:                    #This is the conditional statement.
    print(sample_rate)
else:
    print('less than')

输出 ： less than

t = True
f = True

if t:
    print("Now you see me")
if f:
    print("Now you don't")

输出 ：
Now you see me
Now you don't

f = open('dq_unisex_names.csv', 'r')
names = f.read()
names_list = names.split('\n')
first_five = names_list[0:5]
print (first_five)

输出 ： ['Casey,176544.3281', 'Riley,154860.6652', 'Jessie,136381.8307', 'Jackie,132928.7887', 'Avery,121797.4195']

#Convert The List Of Strings To A List Of Lists
f = open('dq_unisex_names.csv', 'r')
names = f.read()
names_list = names.split('\n')
nested_list = []
for line in names_list:
    comma_list = line.split(',')
    nested_list.append(comma_list)
print(nested_list[0:5])

输出 ：
[['Casey', '176544.3281'], ['Riley', '154860.6652'], ['Jessie', '136381.8307'], ['Jackie', '132928.7887'], ['Avery', '121797.4195']]

nested_list = [['Casey', '176544.3281'], ['Riley', '154860.6652'], ['Jessie', '136381.8307'], ['Jackie', '132928.7887'], ['Avery', '121797.4195']]
numerical_list = []
for line in nested_list:
    name = line[0]
    count = float(line[1])
    new_list = [name, count]
    numerical_list.append(new_list)
print(numerical_list[0:5])

输出 ：
[['Casey', 176544.3281], ['Riley', 154860.6652], ['Jessie', 136381.8307], ['Jackie', 132928.7887], ['Avery', 121797.4195]]

weather_data = []
f = open("la_weather.csv", 'r')
data = f.read()
rows = data.split('\n')
#print (rows)
for row in rows:
    split_row = row.split(",")
    weather_data.append(split_row)
print (weather_data)

输出 ：
[['1', 'Sunny'], ['2', 'Sunny'], ['3', 'Sunny'], ['4', 'Sunny'], ['5', 'Sunny'], ['6', 'Rain'], ['7', 'Sunny'], ['8', 'Sunny'], ['9', 'Fog'], ['10', 'Rain']]

weather = []
for row in weather_data:
    weather.append(row[1])
print (weather)
f.close()

输出 ：
['Sunny', 'Sunny', 'Sunny', 'Sunny', 'Sunny', 'Rain', 'Sunny', 'Sunny', 'Fog', 'Rain']

#find a value
animals = ["cat", "dog", "rabbit"]
for animal in animals:
    if animal == "cat":
        print("Cat found")

输出 ： Cat found

animals = ["cat", "dog", "rabbit"]
if "cat" in animals:
    print("Cat found")

输出 ： Cat found

animals = ["cat", "dog", "rabbit"]
cat_found = "cat" in animals
print (cat_found)

输出 ： True

#Dictionaries
students = ["Tom", "Jim", "Sue", "Ann"]
scores = [70, 80, 85, 75]

indexes = [0,1,2,3]
name = "Sue"
score = 0
for i in indexes:
    if students[i] == name:
        score = scores[i]
print(score)

输出 ： 85

scores = {} #key value
print (type(scores))
scores["Jim"] = 80
scores["Sue"] = 85
scores["Ann"] = 75
#print (scores.keys())
print (scores)
print (scores["Sue"])

输出 ：
<class 'dict'>
{'Ann': 75, 'Sue': 85, 'Jim': 80}
85

students = {}
students["Tom"] = 60
students["Jim"] = 70
print (students)

students = {
    "Tom": 60,
    "Jim": 70
}
print (students)

输出 ：
{'Tom': 60, 'Jim': 70}
{'Tom': 60, 'Jim': 70}

students = {
    "Tom": 60,
    "Jim": 70
}
students["Tom"] = 65
print (students)
students["Tom"] = students["Tom"] + 5
print (students)

输出 ：
{'Tom': 65, 'Jim': 70}
{'Tom': 70, 'Jim': 70}

students = {
    "Tom": 60,
    "Jim": 70
}
print ('Tom' in students)

输出 ： False

pantry = ["apple", "orange", "grape", "apple", "orange", "apple", "tomato", "potato", "grape"]
pantry_counts = {}

for item in pantry:
    if item in pantry_counts:
        pantry_counts[item] = pantry_counts[item] + 1
    else:
        pantry_counts[item] = 1
print (pantry_counts)

输出 ： {'potato': 1, 'apple': 3, 'tomato': 1, 'orange': 2, 'grape': 2}

def printHello():
    
    print ('hello python')
    
def printNum():
    
    for i in range(0,10):
        print (i)
    return
        
def add(a,b):
    return a+b
    
#printHello()
#print (printNum())
print (add(1,2))

输出 ： 3

def printHello():
    print ('hello')
    
def printNum():
    for i in range(0,10):
        print (i)
    return
        
def add(a,b):
    return a+b
    
print (printHello())
print (printNum())
print (add(1,2))

输出 ：

hello
None
0
1
2
3
4
5
6
7
8
9
None
3