10个易被忽视但应掌握的Python基本用法

mynumber = 5
 
print "Python 2:"
print "The number is %d" % (mynumber)
print mynumber / 2,
print mynumber // 2
 
from __future__ import print_function
from __future__ import division
 
print('nPython 3:')
print("The number is {}".format(mynumber))
print(mynumber / 2, end=' ')
print(mynumber // 2)
 
Python 2:
The number is 5
2 2
 
Python 3:
The number is 5
2.5 2

from __future__ import braces
File "", line 1
from __future__ import braces
SyntaxError: not a chance

mylist = ["It's", 'only', 'a', 'model']
 
for index, item in enumerate(mylist):
  print(index, item)
 
0 It's
1 only
2 a
3 model

mynumber = 3
 
if 4 > mynumber > 2:
  print("Chained comparison operators work! n" * 3)
 
Chained comparison operators work!
Chained comparison operators work!
Chained comparison operators work!

from collections import Counter
from random import randrange
import pprint
 
mycounter = Counter()
 
for i in range(100):
  random_number = randrange(10)
  mycounter[random_number] += 1
 
for i in range(10):
  print(i, mycounter[i])
 

0 10
1 10
2 13
3 6
4 6
5 11
6 10
7 14
8 12
9 8

my_phrase = ["No", "one", "expects", "the", "Spanish", "Inquisition"]
my_dict = {key: value for value, key in enumerate(my_phrase)}
print(my_dict)
reversed_dict = {value: key for key, value in my_dict.items()}
print(reversed_dict)

{'Inquisition': 5, 'No': 0, 'expects': 2, 'one': 1, 'Spanish': 4, 'the': 3}
{0: 'No', 1: 'one', 2: 'expects', 3: 'the', 4: 'Spanish', 5: 'Inquisition'}

import subprocess
output = subprocess.check_output('dir', shell=True)
print(output)

Volume in drive C is OS
Volume Serial Number is [REDACTED]
Directory of C:UsersDavidDocuments[REDACTED]
 
2014-11-26 06:04 AM       .
2014-11-26 06:04 AM       ..
2014-11-23 11:47 AM       .git
2014-11-26 06:06 AM       .ipynb_checkpoints
2014-11-23 08:59 AM       CCCma
2014-09-03 06:58 AM      19,450 colorbrewdict.py
2014-09-03 06:58 AM      92,175 imagecompare.ipynb
2014-11-23 08:41 AM       Japan_Earthquakes
2014-09-03 06:58 AM       1,100 LICENSE
2014-09-03 06:58 AM       5,263 monty_monte.ipynb
2014-09-03 06:58 AM      31,082 pocket_tumblr_reddit_api.ipynb
2014-11-26 06:04 AM       3,211 README.md
2014-11-26 06:14 AM      19,898 top_10_python_idioms.ipynb
2014-09-03 06:58 AM       5,813 tree_convert_mega_to_gexf.ipynb
2014-09-03 06:58 AM       5,453 tree_convert_mega_to_json.ipynb
2014-09-03 06:58 AM       1,211 tree_convert_newick_to_json.py
2014-09-03 06:58 AM      55,970 weather_ML.ipynb
       11 File(s)    240,626 bytes
        6 Dir(s) 180,880,490,496 bytes free

my_dict = {'name': 'Lancelot', 'quest': 'Holy Grail', 'favourite_color': 'blue'}
 
print(my_dict.get('airspeed velocity of an unladen swallow', 'African or European&＃63;n'))
 
for key, value in my_dict.iteritems():
  print(key, value, sep=": ")
 
African or European&＃63;
 
quest: Holy Grail
name: Lancelot
favourite_color: blue

a = 'Spam'
b = 'Eggs'
 
print(a, b)
 
a, b = b, a
 
print(a, b)
 
Spam Eggs
Eggs Spam

my_dict = {'That': 'an ex-parrot!'}
 
help(my_dict)

Help on dict object:
 
class dict(object)
 | dict() -> new empty dictionary
 | dict(mapping) -> new dictionary initialized from a mapping object's
 | (key, value) pairs
 | dict(iterable) -> new dictionary initialized as if via:
 | d = {}
 | for k, v in iterable:
 | d[k] = v
 | dict(**kwargs) -> new dictionary initialized with the name=value pairs
 | in the keyword argument list. For example: dict(One=1, two=2)
 |
 | Methods defined here:
 |
 | __cmp__(...)
 | x.__cmp__(y) <==> cmp(x,y)
 |
 | __contains__(...)
 | D.__contains__(k) -> True if D has a key k, else False
 |
 | __delitem__(...)
 | x.__delitem__(y) <==> del x[y]
 |
 | __eq__(...)
 | x.__eq__(y) <==> x==y
 |
 
[TRUNCATED FOR SPACE]
 
 |
 | update(...)
 | D.update([E, ]**F) -> None. Update D from dict/iterable E and F.
 | If E present and has a .keys() method, does: for k in E: D[k] = E[k]
 | If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v
 | In either case, this is followed by: for k in F: D[k] = F[k]
 |
 | values(...)
 | D.values() -> list of D's values
 |
 | viewitems(...)
 | D.viewitems() -> a set-like object providing a view on D's items
 |
 | viewkeys(...)
 | D.viewkeys() -> a set-like object providing a view on D's keys
 |
 | viewvalues(...)
 | D.viewvalues() -> an object providing a view on D's values
 |
 | ----------------------------------------------------------------------
 | Data and other attributes defined here:
 |
 | __hash__ = None
 |
 | __new__ =
 | T.__new__(S, ...) -> a new object with type S, a subtype of T

my_long_text = ("We are no longer the knights who say Ni! "
        "We are now the knights who say ekki-ekki-"
        "ekki-p'tang-zoom-boing-z'nourrwringmm!")
print(my_long_text)

we are no longer the knights who say Ni! We are now the knights who say ekki-ekki-ekki-p'tang-zoom-boing-z'nourrwringmm!