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-rw-r--r--LectureNotesOnPython.rst391
1 files changed, 326 insertions, 65 deletions
diff --git a/LectureNotesOnPython.rst b/LectureNotesOnPython.rst
index 8505e95..80e9d5e 100644
--- a/LectureNotesOnPython.rst
+++ b/LectureNotesOnPython.rst
@@ -263,45 +263,45 @@ a = [1, 2] 可以原地修改a[0] = 2
数与格式化显示
-------------------------
-| x = 3.1415926
-
-| print('%4.0f' % (x))
-| print('%4.1f' % (x))
-| print('%4.2f' % (x))
-| print('%4.3f' % (x))
-| print('%4.4f' % (x))
-
-
-| print('%6.0f' % (x))
-| print('%6.1f' % (x))
-| print('%6.2f' % (x))
-| print('%6.3f' % (x))
-| print('%6.4f' % (x))
-
-
-| print('%.0f' % (x))
-| print('%.1f' % (x))
-| print('%.2f' % (x))
-| print('%.3f' % (x))
-| print('%.4f' % (x))
-| print('%.5f' % (x))
-| print('%.6f' % (x))
-| print('%.7f' % (x))
-| print('%.8f' % (x))
-| print('%.9f' % (x))
-| print('%.15f' % (x))
-| print('%.16f' % (x))
-| print('%.17f' % (x))
-| print('%.18f' % (x))
-
-| print('%4.f' % (x))
-| print('%5.f' % (x))
-| print('%6.f' % (x))
-| print('%7.f' % (x))
-| print('%8.f' % (x))
-
-| print('%f' % (x))
-
+ | x = 3.1415926
+
+ | print('%4.0f' % (x))
+ | print('%4.1f' % (x))
+ | print('%4.2f' % (x))
+ | print('%4.3f' % (x))
+ | print('%4.4f' % (x))
+
+
+ | print('%6.0f' % (x))
+ | print('%6.1f' % (x))
+ | print('%6.2f' % (x))
+ | print('%6.3f' % (x))
+ | print('%6.4f' % (x))
+
+
+ | print('%.0f' % (x))
+ | print('%.1f' % (x))
+ | print('%.2f' % (x))
+ | print('%.3f' % (x))
+ | print('%.4f' % (x))
+ | print('%.5f' % (x))
+ | print('%.6f' % (x))
+ | print('%.7f' % (x))
+ | print('%.8f' % (x))
+ | print('%.9f' % (x))
+ | print('%.15f' % (x))
+ | print('%.16f' % (x))
+ | print('%.17f' % (x))
+ | print('%.18f' % (x))
+
+ | print('%4.f' % (x))
+ | print('%5.f' % (x))
+ | print('%6.f' % (x))
+ | print('%7.f' % (x))
+ | print('%8.f' % (x))
+
+ | print('%f' % (x))
+
字符串（Strings）
@@ -535,8 +535,8 @@ def f(x):
list(map(f, [1,2]]))
+filter方法，从几个值中选择符合条件的几个值。
-filter方法，从几个值中选择符合条件的几个值
| def f(x):
| if x % 2 == 0:
@@ -647,7 +647,45 @@ TDD - Test-driven Development
测试驱动开发。 My favourite。 刺激有挑战性。 帮助厘清需求。 帮助编写代码。
-推荐使用pytest。如何安装？ 使用命令 ``pip install pytest``
+推荐使用pytest。如何安装？ 使用命令 ``pip install pytest``。
+
+在 ``test_cases.py`` 写如下测试用例。然后在命令行运行： ``python -m pytest test_cases.py`` 。
+
+.. code:: python
+
+ # Copyright (c) Hui Lan 2019
+
+ import random
+ import string
+
+ def make_password(n):
+ '''
+ Return a string of length n consisting of a combination of
+ letters, digits and special characters. Note that each password
+ must have at least one lower case letter, one upper case letter,
+ one digit and one special charater. Return an empty string if n
+ is less than 4.
+ '''
+
+ if n < 4:
+ return ''
+
+ password = random.choice(string.ascii_lowercase) + \
+ random.choice(string.ascii_uppercase) + \
+ random.choice(string.digits) + \
+ random.choice(string.punctuation) + \
+ ''.join([random.choice(string.ascii_letters + string.digits + string.punctuation) for i in range(n-4)])
+
+ return ''.join(random.sample(password, n)) # shuffle password then return
+
+
+
+
+ if __name__ == '__main__':
+ for n in range(0,20):
+ pwd = make_password(n)
+ print(pwd)
+
@@ -697,39 +735,262 @@ item的顺序不可预测，不是按照创建时的顺序。
练习：给定一个字符串，数出每个字母出现的频率。
- | def histogram(s):
- | ''' Cannot pass any test cases. '''
- | pass
+.. code:: python
+
+ def histogram(s):
+ ''' Cannot pass any test cases. '''
+ pass
- | def histogram(s):
- | ''' Can pass the test case in which s is an empty string. '''
- | d = {}
- | return d
+ def histogram(s):
+ ''' Can pass the test case in which s is an empty string. '''
+ d = {}
+ return d
- | def histogram(s):
- | ''' Can pass the test cases in which all characters in s are unique. '''
- | d = {}
- | for c in s:
- | d[c] = 1
- | return d
+ def histogram(s):
+ ''' Can pass the test cases in which all characters in s are unique. '''
+ d = {}
+ for c in s:
+ d[c] = 1
+ return d
- | def histogram(s):
- | ''' Can pass all test cases. '''
- | d = {}
- | for c in s:
- | if c not in d:
- | d[c] = 1
- | else:
- | d[c] += 1
- | return d
+ def histogram(s):
+ ''' Can pass all test cases. '''
+ d = {}
+ for c in s:
+ if c not in d:
+ d[c] = 1
+ else:
+ d[c] += 1
+ return d
- | h = histogram('good')
- | print(h)
+ h = histogram('good')
+ print(h)
练习：给定一个字符串，数出每个单词出现的频率。
+练习：给定一个新闻文本，数出每个单词出现的频率。考虑以下方面，（1）只考虑字典里有的单词。（2）单词周围如有标点符号，要先移除。
+
+.. code:: python
+
+ # Copyright (C) 2019 Hui Lan
+ # The following line fixes SyntaxError: Non-UTF-8 code starting with ...
+ # coding=utf8
+
+ def file2lst(fname):
+ ''' Return a list where each element is a word from fname. '''
+ L = []
+ f = open(fname)
+ for line in f:
+ line = line.strip()
+ lst = line.split()
+ for x in lst:
+ L.append(x)
+ f.close()
+ return L
+
+
+ def lst2dict(lst):
+ ''' Return a dictionary given list lst. Each key is an element in the lst.
+ The value is always 1.'''
+ d = {}
+ for w in lst:
+ d[w] = 1
+ return d
+
+
+ import string
+ def remove_punctuation(s):
+ p = ',.:’“”' + string.punctuation
+ t = ''
+ for c in s:
+ if not c in p:
+ t += c
+ elif c == '’': # handle the case such as May’s
+ return t
+ return t
+
+ def word_frequency(fname, english_dictionary):
+ ''' Return a dictionary where each key is a word both in the file fname and in
+ the dictionary english_dictionary, and the corresponding value is the frequency
+ of that word.'''
+ d = {}
+ L = file2lst(fname)
+ for x in L:
+ x = remove_punctuation(x.lower())
+ if x in english_dictionary:
+ if not x in d:
+ d[x] = 1
+ else:
+ d[x] += 1
+ return d
+
+
+ def sort_by_value(d):
+ ''' Return a sorted list of tuples, each tuple containing a key and a value.
+ Note that the tuples are order in descending order of the value.'''
+ import operator
+ lst = sorted(d.items(), key=operator.itemgetter(1), reverse=True)
+ return lst
+
+
+ if __name__ == '__main__':
+ ed = lst2dict(file2lst('words.txt')) # from http://greenteapress.com/thinkpython2/code/words.txt
+ d = word_frequency('brexit-news.txt', ed)
+ lst = sort_by_value(d)
+ for x in lst:
+ print('%s (%d)' % (x[0], x[1]))
+
+
+
+key与value互换
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+注意到在原来的字典中一个value可能对应多个key的值。比如 ``d = {'a':1, 'b':2, 'c':2}`` 中，2就对应两个key，'b'与'c'。
+
+
+.. code:: python
+
+ def inverse_dictionary(d):
+ d2 = {}
+ for k in d:
+ v = d[k]
+ if not v in d2:
+ d2[v] = [k]
+ else:
+ d2[v].append(k)
+ return d2
+
+
+
+ d = {'a':1, 'b':2, 'c':2}
+ d2 = inverse_dictionary(d)
+ print(d2)
+
+
+练习： 用 ``inverse_dictionary`` 对上面 ``d = word_frequency('brexit-news.txt', ed)`` 产生的 ``d`` 进行转化。然后按照单词出现频率从高到低把所有单词都显示出来。每行显示一个频率内的所有单词。
+
+
+.. code:: python
+
+ d2 = inverse_dictionary(d)
+ for k in sorted(d2.keys(), reverse=True):
+ print('%d %s' % (k, ' '.join(d2[k])))
+
+
+练习： 使用 ``setdefault`` 方法对上面的 ``inverse_dictionary`` 进行简化 （减少行数）。
+
+
+.. code:: python
+
+
+
+ def inverse_dictionary(d):
+ d2 = {}
+ for k in d:
+ v = d[k]
+ d2.setdefault(v, []).append(k)
+
+ return d2
+
+
+
+
+函数
+------
+
+函数 ``unique_words`` 与 ``unique_words2`` 哪个运行速度快？
+
+.. code:: python
+
+ def unique_words(lst):
+ d = {}
+ for x in lst:
+ d[x] = 1
+ return sorted(d.keys())
+
+ def unique_words2(lst):
+ return sorted(list(set(lst)))
+
+
+ N = 10000000
+ print(unique_words(['hello', 'world', 'am', 'he'] * N))
+ print(unique_words2(['hello', 'world', 'am', 'he'] * N))
+
+
+
+局部变量
+~~~~~~~~~~~~~~~~
+
+在函数之内。函数执行结束，局部变量消失。
+
+
+全局变量
+~~~~~~~~~~~~~~~~
+
+全局变量位于函数之外，模块之内。全局变量对所有模块内的函数可见（可读）。如果在函数内要对全局变量重新赋值，那么要先用 ``global`` 声明之 （declare）。
+
+
+.. code:: python
+
+ verbose = True
+
+ def example1():
+ if verbose:
+ print('Running example1')
+
+ def example2():
+ verbose = False # a NEW local variable verbose
+ if verbose:
+ print('Running example2')
+
+ def example3():
+ global verbose # I am actually going to use the global variable verbose; don't create a local one.
+ verbose = False
+ if verbose:
+ print('Running example3')
+
+
+
+ print(verbose)
+ example1()
+
+ print(verbose)
+ example2()
+ example1()
+
+ print(verbose)
+ example3()
+ example1()
+
+ print(verbose)
+
+
+
+全局的列表与字典，如果只需改变其内容，而不是重新赋值，则不需要用 ``global`` 声明。
+
+
+.. code:: python
+
+ record = {'s1':65, 's2':60}
+
+ def add_score(student, score):
+ record[student] = score
+
+
+ print(record)
+ add_score('s3', 75)
+ print(record)
+
+
+练习： 定义一个函数 ``empty_dict`` 清空字典 ``record``。 要求: 不能用 ``return`` 语句。 提示： 可以用 ``pop`` 方法， 或者直接给 ``record`` 赋值 ``{}`` 。
+
+
+函数执行顺序
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
参考
------
generated by cgit v1.2.1 (git 2.18.0) at 2025-03-15 20:35:29 +0000