一、前言

Python语法简单，大多数情况下，根据单词的意思就可以猜测出程序的功能。

在介绍Python语法之前，先看一些Pyhton代码的案例，这些案例都很简单，可以在PyChram中运行。

打开PyCharm，我们直接新建一个Python文件（右键工程文件夹(pythonProject)-->New-->Python File）

新建Python文件

然后弹出窗口，给文件命名，这里命名为test，按回车创建。

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于是工程文件夹下就多了一个test.py文件，我们就在这里写代码。

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编写完成后，右键test.py，点击运行（Run）。

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二、从一行代码开始运行Python程序

代码来自：https://wiki.python.org/moin/SimplePrograms

1行：输出信息

代码：

print('Hello, world!')

运行结果：

Hello, world!

2行：输入信息

代码：

name = input('What is your name?\n')
print ('Hi, %s.' % name)

运行后，PyCharm下面的控制台会打印提示消息，What is your name?

我们点一下这句话的下面，然后就可以输入名字了。

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image8.png

(输入完，按回车表示输入结束)

程序得到信息，并将该信息输出：

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3行：for循环

代码：

friends = ['john', 'pat', 'gary', 'michael']
for i, name in enumerate(friends):
    print(f"friend {i} is {name}")

运行结果：

friend 0 is john
friend 1 is pat
friend 2 is gary
friend 3 is michael

4行：实现斐波那契数

代码：

parents, babies = (1, 1)
while babies < 100:
    print(f'This generation has {babies} babies')
    parents, babies = (babies, parents + babies)

运行结果：

This generation has 1 babies
This generation has 2 babies
This generation has 3 babies
This generation has 5 babies
This generation has 8 babies
This generation has 13 babies
This generation has 21 babies
This generation has 34 babies
This generation has 55 babies
This generation has 89 babies

5行：函数（Functions）

代码：

def greet(name):
    print('Hello', name)
greet('Jack')
greet('Jill')
greet('Bob')

运行结果：

Hello Jack
Hello Jill
Hello Bob

6行：导入库，使用库的函数进行字符串匹配。

代码：

import re
for test_string in ['555-1212', 'ILL-EGAL']:
    if re.match(r'^\d{3}-\d{4}$', test_string):
        print(test_string, 'is a valid US local phone number')
    else:
        print(test_string, 'rejected')

运行结果：

555-1212 is a valid US local phone number
ILL-EGAL rejected

7行：字典，生成器表达式

代码：

prices = {'apple': 0.40, 'banana': 0.50}
my_purchase = {
    'apple': 1,
    'banana': 6}
grocery_bill = sum(prices[fruit] * my_purchase[fruit]
                   for fruit in my_purchase)
print(f'I owe the grocer {grocery_bill:.2f}$')

运行结果：

I owe the grocer 3.40$

8行：从命令行读入。程序实现了一个加法器

# This program adds up integers that have been passed as arguments in the command line
import sys
try:
    total = sum(int(arg) for arg in sys.argv[1:])
    print ('sum =', total)
except ValueError:
    print ('Please supply integer arguments')为什么只有7行呢，因为第8行在命令行中输入：

在命令行中输入：

 python test.py 1 2 3 4

点击下面的Terminal，进入命令行，输入代码。执行test.py程序。

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9行（#开头的注释不算，11-2=9）：读取文件

代码：

# indent your Python code to put into an email
import glob

# glob supports Unix style pathname extensions
python_files = glob.glob('*.py')
for file_name in sorted(python_files):
    print('    ------' + file_name)
    with open(file_name) as f:
        for line in f:
            print('    ' + line.rstrip())
    print()

运行结果：

输出了该目录下py文件内容。

10行：获取当前时间（不算activities及其上下空格，activities相当于是数据）

代码：

from time import localtime

activities = {8: 'Sleeping',
              9: 'Commuting',
              17: 'Working',
              18: 'Commuting',
              20: 'Eating',
              22: 'Resting' }
time_now = localtime()
hour = time_now.tm_hour

for activity_time in sorted(activities.keys()):
    if hour < activity_time:
        print (activities[activity_time])
        break
else:
    print ('Unknown, AFK or sleeping!')

运行结果：

我运行的时间是上午10:42，所以对应的是：

Working

11行：三引号字符串，while循环

代码：

REFRAIN = '''
%d bottles of beer on the wall,
%d bottles of beer,
take one down, pass it around,
%d bottles of beer on the wall!
'''
bottles_of_beer = 9
while bottles_of_beer > 1:
    print(REFRAIN % (bottles_of_beer, bottles_of_beer,
                     bottles_of_beer - 1))
    bottles_of_beer -= 1

运行结果：

每次句子中的bottles_of_beer减一。

12行：类。创建一个银行账户，进行存钱取钱。

代码：

class BankAccount(object):
    def __init__(self, initial_balance=0):
        self.balance = initial_balance
    def deposit(self, amount):
        self.balance += amount
    def withdraw(self, amount):
        self.balance -= amount
    def overdrawn(self):
        return self.balance < 0
my_account = BankAccount(15)
my_account.withdraw(50)
print (my_account.balance, my_account.overdrawn()):

运行结果：

-35 True

13行：使用unittest进行单元测试（Unit testing）。下面代码测试了一个取中位数的功能median。

self.assertEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7)语句，是判断函数median的结果是否和预期结果7相同。

代码：

import unittest
def median(pool):
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[int((size - 1) / 2)]
    else:
        return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2
class TestMedian(unittest.TestCase):
    def testMedian(self):
        self.assertEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7)
if __name__ == '__main__':
    unittest.main()

运行结果：

D:/PY_TEST/pythonProject/test.py
Testing started at 10:49 ...
Launching unittests with arguments python -m unittest D:/PY_TEST/pythonProject/test.py in D:\PY_TEST\pythonProject

Ran 1 test in 0.002s

OK

14行：文档测试（ Doctest-based testing）

def median(pool):
    '''Statistical median to demonstrate doctest.
    >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
    6 #change to 7 in order to pass the test
    '''
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[int((size - 1) / 2)]
    else:
        return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2
if __name__ == '__main__':
    import doctest
    doctest.testmod()

运行结果：错误，预期 6 #change to 7 in order to pass the test，得到值7。

Failure
<Click to see difference>

**********************************************************************
File "D:\PY_TEST/pythonProject\test.py", line 3, in test.median
Failed example:
    median([2, 9, 9, 7, 9, 2, 4, 5, 8])
Expected:
    6 #change to 7 in order to pass the test
Got:
    7

说明文档错误，修改代码第4行：

def median(pool):
    '''Statistical median to demonstrate doctest.
    >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
    7
    '''
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[int((size - 1) / 2)]
    else:
        return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2
if __name__ == '__main__':
    import doctest
    doctest.testmod()

运行结果：没有错误，表示通过。

Testing started at 10:57 ...

Process finished with exit code 0