Learning Python(2)

File

• Read file

with open('pai.txt') as file_object:
    contents=file_object.read()
    print(content.strip())

with open('pai.txt') as file_object:
    for line in file_object:
        print(line.rstrip())

• keyword with means there is a file manager to make the file will always be close when the code block is end.

• python read everything in file in string. if there are other data type, use type cast method like int(), float().

• Wirte file

with open('pai.txt','w') as file_object:
    file_object.writelines("I like pie!")

• the second para
  ='w' writemode
  ='r' readmode Default Mode
  ='a' appendmode
  ='r+' both write and read

• only str can be write into file, use str() to cast other data type to str.

Exception

• try-except-else block:

first_num=input("First number:")
second_num=input("Second number:")
try:
    result=float(first_num)/float(second_num)
except Exception: #ZeroDivisionError
    print("you can't divide by zero")
else:
    print("Result is "+str(result))

• pass means do nothing when finding an exception

Save data

• save and load data in json

import json
numbers=[2,3,4,5,6,7]
numbers2=[]
filename='numbers.json'
with open(filename,'r+') as json_obj:
    json.dump(numbers,json_obj)
with open(filename) as json_obj:
    numbers2=json.load(json_obj)
print(numbers2)

Test

• test a method

#getname.py
def get_formatted_name(first,last):
    """Generate a neatly formatted full name"""
    full_name = first+' '+last
    return str(full_name).title()

#test.py
import unittest
from getname get_formatted_name
class NameTestCase(unittest.TestCase):
    """测试"""
    def test_first_last_name(self):
        """能够正确的处理janis jpplin嘛？"""
        formatted_name=get_formatted_name('janis','joplin')
        self.assertEqual(formatted_name,'Janis Joplin')
unittest.main()

• assert a method

• test a class

#survey.py
class AnoumousSurvey():
    """匿名问卷调查"""
    def __init__(self,question):
        self.question=question
        self.responses=[]
    def show_quesiton(self):
        """show quesiton"""
        print(self.question)
    def store_response(self,new_response):
        self.responses.append(new_response)
    def show_results(self):
        print("Survey results:")
        for response in self.responses:
            print('- '+response)

#test.py
from survey import AnoumousSurvey
import unittest
class TestAS(unittest.TestCase):
    """test for AnoumousSurvey"""
    def test_store_single_response(self):
        """测试单个答案是否能被存储"""
        question="What language did you like most?"
        my_survey=AnoumousSurvey(question)
        my_survey.store_response('English')
        self.assertIn('English',my_survey.responses)
unittest.main()

Closure

• Closure is a function that hold the outer variations

def gen_counter(name):
    count=[0]
    def counter():
        count[0] += 1
        print('Hello '+name+','+str(count[0])+' access!')
    return counter
c=gen_counter('master')
c()
c()
c()
#output:
Hello master,1 access!
Hello master,2 access!
Hello master,3 access!
#variation 'count' will only be access by counter(), so it's very safe