Python Beginner Note 2 – Basic Rules

#　　-　　For note making in the program,

the sentence after # would not be a part of the program while running.

The Rules in Naming Variables:

Variables names must start with a letter or an underscore, such as:

• _underscore　　　(O)
• underscore_　　　(O)
• under-score　　　(X)

The remainder of your variable name may consist of letters, numbers and underscores.

• password1　　　　(O)
• n00b　　　　　  　(O)
• un_der_scores　   (O)
• 1password　　　　(X)

Names are case sensitive.

• case_sensitive, CASE_SENSITIVE, and Case_Sensitive are each a different variable.

Reserved words can not be named as other variables

Here’s a list of reserved words but not all included:

• b = 5566　　　(O)
• break = 5566   (X)

Types of literal:

• string　　　　　　e.g. agenda, python5566
• bytes
• integer　　　　 　e.g. 5566
• floating-point  　e.g. 5.566
• imaginary

Types of data:

• int　　　　　　　　e.g. 5566
• float　　　　　　　e.g. 5.566
• complex　　　　　e.g. 556+6j
• str　　　　　　　　e.g. python5566
• bytes
• bytearray
• list　　　　　　   　e.g. [1,2,3,4,5], [1,2,(3),[4,5]]
• tuple　　　　　   　e.g. (1,2,3,4,5), (1,2,(3),[4,5])
• set　　　　　　　   e.g. {1,2,3,4,5} == {1,1,1,1,1,2,3,4,5,5}
• dict　{key:value}   e.g. {1:abba, 2:Bb}

Sub-functions used in ‘list’ data:

Operation	Result	Notes
s[i] = x	item i of s is replaced by x
s[i:j] = t	slice of s from i to j is replaced by the contents of the iterable t
del s[i:j]	same as s[i:j] = []
s[i:j:k] = t	the elements of s[i:j:k] are replaced by those of t	(1)
del s[i:j:k]	removes the elements of s[i:j:k] from the list
s.append(x)	appends x to the end of the sequence (same ass[len(s):len(s)] = [x])
s.clear()	removes all items from s (same as del s[:])	(5)
s.copy()	creates a shallow copy of s (same as s[:])	(5)
s.extend(t) or s += t	extends s with the contents of t (for the most part the same as s[len(s):len(s)] = t)
s *= n	updates s with its contents repeated n times	(6)
s.insert(i, x)	inserts x into s at the index given by i (same as s[i:i]= [x])
s.pop([i])	retrieves the item at i and also removes it from s	(2)
s.remove(x)	remove the first item from s where s[i] == x	(3)
s.reverse()	reverses the items of s in place	(4)

Functions used in ‘set’ data:

Operation	Result	Notes
x | y	bitwise or of x and y
x ^ y	bitwise exclusive or of x and y
x & y	bitwise and of x and y
x << n	x shifted left by n bits	(1)(2)
x >> n	x shifted right by n bits	(1)(3)
~x	the bits of x inverted

方法	描述
s1.intersection(s2)	等於 s1 & s2
s1.union(s2)	等於 s1 | s2
s1.symmetric_difference(s2)	等於 s1 ^ s2
s1.difference(s2)	等於 s1 – s2
s1.issubset(s2)	等於 s1 <= s2
s1.issuperset(s2)	等於 s1 >= s2
s1.isdisjoint(s2)	判斷 s1 與 s2 是否無交集，若無交集，回傳 True
s.copy()	回傳 s 的拷貝

由於 set 型態是可變的，因此有額外兩個新增與刪除元素的方法

方法	描述
s.add(e)	增加 e 為 s 的元素
s.remove(e)	從 s 中刪除元素 e

For ‘dict’ data:

計算	描述
d[key]	從 d 中取得 key 的 value
d[key] = value	將 d 的 key 指定為 value
del d[key]	刪除 d 中 key 所指定的 value
key in d	判斷 key 是否在 d 中
key not in d	判斷 key 是否不在 d 中
iter(d)	回傳由 d 的 key 建立的迭代器
len(d)	回傳 d 的配對資料個數

字典物件有以下的方法 (method)

方法	描述
dict.clear()	清空 dict 的所有配對資料
dict.copy()	回傳 dict 的拷貝
classmethod dict.fromkeys(seq[, value])	由 seq 中的元素構成 key ，每個 key 都給相同的 value 值
dict.get(key[, default])	從 dict 中取得 key 的 value ，若無此 key 則回傳 default ， default 預設為 None
dict.items()	回傳 dict_items 物件，使 key:value 儲存為序對，然後依序儲存在 dict_items 物件中
dict.keys()	回傳 dict_items 物件，使 key 依序儲存在 dict_items 物件中
dict.pop(key[, default])	將 key 的 value 從 dict 移除，若無此 kay ，回傳 default
dict.popitem()	從 dict 移除任意一組 key:value
dict.setdefault(key[, default])	如果 key 在 dict 中，回傳 value 值，反之，將 key:default 加入 dict 之中
dict.update([other])	將 dict 以 other 更新
dict.values()	回傳 dict_items 物件，使 value 依序儲存在 dict_items 物件中

－－－－

Exercise 1:

Solve the questions listed below with data type “set":

List of students who have passed the final Math exam in the class: Tom, John, Mary, Jimmy, Sunny, Amy;

List of students who have passed the final English exam in the class: John, Mary , Tony , Bob , Pony, Tom , Alice

1. print the list of students that passed Math but failed English;
2. print the list of students that passed English but failed Math;
3. print the list of students that passed both; finally
4. print the total number of students.

 

Exercise 2:

Solve the questions listed below with data type “dict" and “list":

Scores of Tom: 80, 100, 90, 95

Scores of John: 100,93,75,80

Store the data with data type ‘dict’ and print the average score of each.

－－

Next: Loops and If functions

－－

Reference:

Coursera

PPT from NTU SPECS course

程式語言教學誌 (In Traditional Chinese)