A string is a sequence of characters. The elements of a string are characters. Empty string ''.(not' ') You can access the characters one at a time with the bracket operator:
>>> fruit = 'banana'
>>> letter = fruit[1]
>>> print(letter)
a
>>> len(fruit)
6
iteration and conditional execution
fruit = 'banana'
for char in fruit:
print(char)
word = 'banana'
count = 0
for letter in word:
if letter == 'a':
count = count + 1
print(count)
String slices
>>> fruit = 'banana'
>>> fruit[1:3]
'an'
>>> fruit[3:]
'ana'
Strings are immutable, lists are mutable
>>> greeting = 'Hello, world!'
>>> greeting[0] = 'J'
TypeError: 'str' object does not
support item assignment
>>> greeting = 'Hello, world!'
>>> new_greeting = 'J' + greeting[1:]
>>> print(new_greeting)
Jello, world!
The in operator
>>> print('a' in 'banana')
True
>>> print('seed' in 'banana')
False
>>> print('x' in ['x','y','z'])
True
String comparison
Comparison operations are useful for putting words in alphabetical order.
>>> print('apple'>'banana')
False
>>> print('ba' > 'banana')
False
>>> print([0, 1, 2] < [0, 3, 4])
True
>>> a_list = ["orange", "apple", "banana"]
>>> a_list.sort()
>>> print(a_list)
['apple', 'banana', 'orange']
Some useful string methods
>>> stuff = 'Hello world'
>>> dir(stuff)
['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__',
'__eq__', '__format__','__ge__', '__getattribute__', '__getitem__',
'__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__',
'__iter__', '__le__','__len__', '__lt__', '__mod__', '__mul__', '__ne__',
'__new__', '__reduce__','__reduce_ex__', '__repr__', '__rmod__', '__rmul__',
'__setattr__', '__sizeof__','__str__', '__subclasshook__', 'capitalize',
'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find',
'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit',
'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle',
'isupper', 'join', 'ljust','lower', 'lstrip', 'maketrans', 'partition',
'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip',
'split', 'splitlines', 'startswith','strip', 'swapcase', 'title', 'translate',
'upper', 'zfill']
>>> help(str.title)
Help on method_descriptor:
title(...)
S.title() -> str
Return a titlecased version of S, i.e. words start with title case
characters, all remaining cased characters have lower case.
.title(), .lower(), .upper()
>>> name = "ada lovelace"
>>> print(name.title())
Ada Lovelace
>>> print(name)
ada lovelace
>>> name = "Ada Lovelace"
>>> print(name.upper())
ADA LOVELACE
>>> print(name.lower())
ada lovelace
.find() searches for the position of a string in another string
>>> word = 'banana'
>>> index = word.find('a')
>>> print(index)
1
>>> word.find('na')
2
>>> word.find('na', 3)
4
.startswith() returns the boolean value
>>> line = 'Have a nice day'
>>> line.startswith('h')
False
>>> line.lower()
'have a nice day'
>>> line.lower().startswith('h')
True
Parsing strings
>>> data = 'From stephen.marquard@uct.ac.za Sat Jan 5 09:14:16 2008'
>>> atpos = data.find('@')
>>> print(atpos)
21
>>> sppos = data.find(' ',atpos)
>>> print(sppos)
31
>>> host = data[atpos+1 : sppos]
>>> print(host)
uct.ac.za
.split() break a sentence into words and make a list
>>> s = 'pining for the fjords'
>>> t = s.split()
>>> print(t)
['pining', 'for', 'the', 'fjords']
>>> print(t[2])
the
One can break a word into letters.
>>> s = 'spam'
>>> t = list(s)
>>> print(t)
['s', 'p', 'a', 'm']
Format operator $%$
It allows us to construct strings, replacing parts of the strings with the data stored in variables.
>>> number = 42
>>> print('I have spotted %d camels.' % number)
I have spotted 42 camels.
What if we do not use format operator?
>>> number = 42
>>> print('I have spotted number camels.') #error.
>>> print('I have spotted '+str(number)+' camels.') #not simple
If there is more than one format sequence in the string, use ().
>>> print('In %d years I have spotted %g %s.' % (3, 0.1, 'camels'))
In 3 years I have spotted 0.1 camels.
The number of elements in the tuple must match the number of format sequences in the string. The types of the elements also must match the format sequences.
>>> print('In {} years I spotted {} {}.'.format(3, 0.1, 'camels'))
In 3 years I have spotted 0.1 camels.
>>> print('In {0} years I have spotted {1} {2}.'.format(3, 0.1, 'camels'))
In 3 years I have spotted 0.1 camels.
>>> print('In {1} years I have spotted {0} {2}.'.format(3, 0.1, 'camels'))
In 0.1 years I have spotted 3 camels.
The elements of a string are characters. Empty string ''
Features: Ordered, Immutable, Repeatable
Index and slice are the same with that of lists.
in operator shows the boolean value for whether a string contains a given string. You can compare two strings in Alphabetical order. (Lists can do similar things)
.upper(), lower(), .title(), .find(), .startwith(), .split() (list('string') and list())
Format operator: %d integer, %g float, %s string (use () for more than one format sequence), .format()
A dictionary is like a list, but more general. In a list, the index positions have to be integers; in a dictionary, the indices can be (almost) any type.
>>> x = {} #This is False
>>> print(x)
{}
The empty dictionary can be written as dict(). Similarly, an empty list can be list().
You can think of a dictionary as a mapping between a set of indices (which are called keys) and a set of values.
>>> x['one'] = 'uno'
>>> print(x)
{'one': 'uno'}
In general, the order of items in a dictionary is unpredictable.
>>> x = {'one': 'apple', 'two': 'banana', 'three': 'orange'}
>>> print(x)
{'one': 'apple', 'three': 'orange', 'two': 'banana'}
>>> print(x['two'])
'banana'
Adding New Key-Value Pairs
>>> alien = {}
>>> alien['color'] = 'green'
>>> alien['point'] = 5
>>> print(alien)
{'color': 'green', 'points': 5}
To create a dictionary, start with an empty one, and add the key-value pairs. The keys should be immutable and there is no repeated key. Lists cannot be keys in the dictionary.
Modifying Values in a Dictionary
>>> alien['color'] = 'yellow'
>>> print(alien)
{'color': 'yellow', 'points': 5}
Removing Key-Value Pairs
>>> del alien['points']
>>> print(alien)
{'color': 'yellow'}
Merge two dictionaries
>>> dict1 = { "name":"owen", "age": 18 }
>>> dict2 = { "birthday": "1999-11-22"}
>>> x = dict( dict1, **dict2 )
>>> print(x)
{'name': 'owen', 'age': 18, 'birthday': '1999-11-22'}
>>> a = { 'x' : 1 , 'y' : 2 }
>>> b = { 'y' : 3 , 'z' : 4 }
>>> c = dict(a,**b)
>>> print(c)
{'x': 1, 'y': 3, 'z': 4}
The in operator works on dictionaries. (keys)
>>> x = {'one': 'apple', 'two': 'banana', 'three': 'orange'}
>>> 'one' in x
True
>>> 'uno' in x
False
To see whether something appears as a value in a dictionary, you can use the method .values().
>>> x = {'one': 'apple', 'two': 'banana', 'three': 'orange'}
>>> print('orange' in x.values())
True
The len function works on dictionaries; it returns the number of key-value pairs
>>> x = {'one': 'apple', 'two': 'banana', 'three': 'orange'}
>>> len(x)
3
word = 'banana'
d = dict()
for c in word:
if c not in d:
d[c] = 1
else:
d[c] = d[c] + 1
print(d)
{'b': 1, 'a': 3, 'n': 2}
>>> counts = { 'chuck' : 1 , 'annie' : 42, 'jan': 100}
>>> print(counts.get('jan', 0)) #0 is the default value
100
>>> print(counts.get('anni', 1550))
1550
word = 'banana'
d = dict()
for c in word:
d[c] = d.get(c,0) + 1
print(d)
Looping Through All Key-Value Pairs
favorite = {
'jen': 'python',
'sarah': 'c',
'edward': 'ruby',
}
for x, y in favorite.items():
print(x, y)
for x, y in list(favorite.items()):
print(x, y)
jen python
sarah c
edward ruby
Looping Through All the Keys in a Dictionary
favorite = {
'jen': 'python',
'sarah': 'c',
'edward': 'ruby',
}
for x in favorite.keys():
print(x.title())
#for x in list(favorite.keys()):
Jen
Sarah
Edward
friends = ['sarah', 'jen']
for x in favorite.keys():
if x in friends:
print(x.title()+" "+favorite[x])
Jen python
Sarah c
Looping Through All Values in a Dictionary
favorite = {
'jen': 'python',
'sarah': 'c',
'edward': 'ruby',
}
for y in favorite.values():
print(y.title())
#for language in list(favorite.values()):
Python
C
Ruby
You can nest a set of dictionaries inside a list, a list of items inside a dictionary, or even a dictionary inside another dictionary. A list or a dictionary cannot be the key (The key should be immutable).
Dictionaries in a list
alien_0 = {'color': 'green', 'points': 5}
alien_1 = {'color': 'yellow', 'points': 10}
alien_2 = {'color': 'red', 'points': 15}
aliens = [alien_0, alien_1, alien_2]
A List in a Dictionary
pizza = {
'crust': 'thick',
'toppings': ['mushrooms', 'extra cheese'],
}
print(pizza['crust'], pizza['toppings'][1])
thick extra cheese
You can nest a list inside a dictionary any time you want more than one value to be associated with a single key in a dictionary
favorite_languages = {
'jen': ['python', 'ruby'],
'sarah': ['c'],
'edward': ['ruby', 'go'],
'phil': ['python', 'haskell'],
}
print(favorite_languages['jen'][0].title())
Python
A Dictionary in a Dictionary
users = {
'aeinstein': {
'first': 'albert',
'last': 'einstein',
'location': 'princeton',
},
'mcurie': {
'first': 'marie',
'last': 'curie',
'location': 'paris',
},
}
full_name = users['aeinstein']['first']+" "+users['aeinstein']['last']
location = users['aeinstein']['location']
print("Full name: " + full_name.title())
print("Location: " + location.title())
Full name: Albert Einstein
Location: Princeton
Elements are key-value pairs. Empty dictionary {}
Features：unpredictable order, key-value pairs are mutable (keys are immutable, but you can modify values). Do not make repeated keys.
.get() (value or default value)
Looping: .items(), .keys(), .values()
in operator works on keys (but you can use .values())
Nesting: A list of dictionaries, a list in a dictionary, a dictionary in a dictionary
[[2020001, "17 25 26 32 34-04 07"],
[2020002, "03 07 18 25 30-02 07"],
... ,
[2020092, "08 11 17 31 35-07 11"]]
import json
filename = 'lottery.json'
with open(filename) as f:
data = json.load(f)
five_number=[]
for x in data:
position=x[1].find('-')
string_5=x[1][:position]
list_5=string_5.split()
five_number.append(list_5)
d={}
for x in five_number:
for y in x:
d[y]=d.get(y,0)+1
fre=[]
for x,y in d.items():
fre.append([y,x])
fre.sort()
for x in fre:
print(x)