Python基础语法精华，

 

 

 

 

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Python基础语法包括以下内容¶

:

• Data types
  • Numbers
  • Strings
  • Printing
  • Lists
  • Dictionaries
  • Booleans
  • Tuples
  • Sets
• Comparison Operators
• if, elif, else Statements
• for Loops
• while Loops
• range()
• list comprehension
• functions
• lambda expressions
• map and filter
• methods

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Data types¶

Numbers¶

In [1]:

1 + 1 + 5

Out[1]:

7

 

1 * 3

In [2]:

1 / 2

Out[2]:

0.5

In [3]:

2 ** 4

Out[3]:

16

In [4]:

4 % 2

Out[4]:

0

In [5]:

5 % 2

Out[5]:

1

In [6]:

(2 + 3) * (5 + 5)

Out[6]:

50

In [7]:

x = 2
y = 3

In [8]:

z = x + y

In [9]:

z

Out[9]:

5

 

Strings¶

In [10]:

'single quotes'

Out[10]:

'single quotes'

In [11]:

"double quotes"

Out[11]:

'double quotes'

In [12]:

" wrap lot's of other quotes"

Out[12]:

" wrap lot's of other quotes"

In [13]:

# Can not start with number or special characters
name_of_var = 2

 

Printing¶

In [14]:

x = 'hello'

In [15]:

x

Out[15]:

'hello'

 

Variable Assignment¶

In [ ]:   In [ ]:   In [ ]:   In [22]:

print(x)

 

hello

In [23]:

num = 12
name = 'Sam'

In [24]:

print('My number is: {one}, and my name is: {two}'.format(one=num,two=name))

 

My number is: 12, and my name is: Sam

In [ ]:   In [25]:

print('My number is: {}, and my name is: {}'.format(num,name))

 

My number is: 12, and my name is: Sam

 

Lists¶

In [26]:

[1,2,3]

Out[26]:

[1, 2, 3]

In [27]:

['hi',1,[1,2]]

Out[27]:

['hi', 1, [1, 2]]

In [28]:

my_list = ['a','b','c']

In [29]:

my_list.append('d')

In [30]:

my_list

Out[30]:

['a', 'b', 'c', 'd']

In [31]:

my_list[0]

Out[31]:

'a'

In [32]:

my_list[1]

Out[32]:

'b'

In [33]:

my_list[1:]

Out[33]:

['b', 'c', 'd']

In [34]:

my_list[:1]

Out[34]:

['a']

In [35]:

my_list[0] = 'NEW'

In [98]:

my_list

Out[98]:

['NEW', 'b', 'c', 'd']

In [99]:

nest = [1,2,3,[4,5,['target']]]

In [100]:

nest[3]

Out[100]:

[4, 5, ['target']]

In [101]:

nest[3][2]

Out[101]:

['target']

In [102]:

nest[3][2][0]

Out[102]:

'target'

 

Dictionaries¶

In [37]:

d = {'key1':'item1','key2':'item2'}

In [38]:

d

Out[38]:

{'key1': 'item1', 'key2': 'item2'}

In [39]:

d['key1']

Out[39]:

'item1'

 

Booleans¶

In [40]:

True

Out[40]:

True

In [41]:

False

Out[41]:

False

 

Tuples¶

In [42]:

t = (1,2,3)

In [43]:

t[0]

Out[43]:

1

In [44]:

t[0] = 'NEW'

 

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-44-97e4e33b36c2> in <module>()
----> 1t[0] = 'NEW'

TypeError: 'tuple' object does not support item assignment

 

Sets¶

In [45]:

{1,2,3}

Out[45]:

{1, 2, 3}

In [46]:

{1,2,3,1,2,1,2,3,3,3,3,2,2,2,1,1,2}

Out[46]:

{1, 2, 3}

 

Comparison Operators¶

In [47]:

1 > 2

Out[47]:

False

In [48]:

1 < 2

Out[48]:

True

In [49]:

1 >= 1

Out[49]:

True

In [50]:

1 <= 4

Out[50]:

True

In [51]:

1 == 1

Out[51]:

True

In [52]:

'hi' == 'bye'

Out[52]:

False

 

Logic Operators¶

In [53]:

(1 > 2) and (2 < 3)

Out[53]:

False

In [54]:

(1 > 2) or (2 < 3)

Out[54]:

True

In [55]:

(1 == 2) or (2 == 3) or (4 == 4)

Out[55]:

True

 

if,elif, else Statements¶

In [56]:

if 1 < 2:
    print('Yep!')

 

Yep!

In [57]:

if 1 < 2:
    print('yep!')

 

yep!

In [3]:

if 1 < 2:
    print('first1')
else:
    print('last')

 

first1

In [59]:

if 1 > 2:
    print('first')
else:
    print('last')

 

last

In [60]:

if 1 == 2:
    print('first')
elif 3 == 3:
    print('middle')
else:
    print('Last')

 

middle

 

for Loops¶

In [61]:

seq = [1,2,3,4,5]

In [62]:

for item in seq:
    print(item)

 

1
2
3
4
5

In [63]:

for item in seq:
    print('Yep')

 

Yep
Yep
Yep
Yep
Yep

In [64]:

for jelly in seq:
    print(jelly+jelly)

 

2
4
6
8
10

 

while Loops¶

In [65]:

i = 1
while i < 5:
    print('i is: {}'.format(i))
    i = i+1

 

i is: 1
i is: 2
i is: 3
i is: 4

 

range()¶

In [66]:

range(5)

Out[66]:

range(0, 5)

In [67]:

for i in range(5):
    print(i)

 

0
1
2
3
4

In [68]:

list(range(5))

Out[68]:

[0, 1, 2, 3, 4]

 

list comprehension¶

In [69]:

x = [1,2,3,4]

In [70]:

out = []
for item in x:
    out.append(item**2)
print(out)

 

[1, 4, 9, 16]

In [71]:

[item**2 for item in x]

Out[71]:

[1, 4, 9, 16]

 

functions¶

In [72]:

def my_func(param1='default'):
    """
    Docstring goes here.
    """
    print(param1)

In [73]:

my_func

Out[73]:

<function __main__.my_func>

In [74]:

my_func()

 

default

In [75]:

my_func('new param')

 

new param

In [76]:

my_func(param1='new param')

 

new param

In [77]:

def square(x):
    return x**2

In [78]:

out = square(2)

In [79]:

print(out)

 

4

 

lambda expressions¶

In [80]:

def times2(var):
    return var*2

In [81]:

times2(2)

Out[81]:

4

In [82]:

lambda var: var*2

Out[82]:

<function __main__.<lambda>>

 

map and filter¶

In [83]:

seq = [1,2,3,4,5]

In [84]:

map(times2,seq)

Out[84]:

<map at 0x105316748>

In [85]:

list(map(times2,seq))

Out[85]:

[2, 4, 6, 8, 10]

In [86]:

list(map(lambda var: var*2,seq))

Out[86]:

[2, 4, 6, 8, 10]

In [87]:

filter(lambda item: item%2 == 0,seq)

Out[87]:

<filter at 0x105316ac8>

In [88]:

list(filter(lambda item: item%2 == 0,seq))

Out[88]:

[2, 4]

 

methods¶

In [111]:

st = 'hello my name is Sam'

In [112]:

st.lower()

Out[112]:

'hello my name is sam'

In [113]:

st.upper()

Out[113]:

'HELLO MY NAME IS SAM'

In [103]:

st.split()

Out[103]:

['hello', 'my', 'name', 'is', 'Sam']

In [104]:

tweet = 'Go Sports! #Sports'

In [106]:

tweet.split('#')

Out[106]:

['Go Sports! ', 'Sports']

In [107]:

tweet.split('#')[1]

Out[107]:

'Sports'

In [92]:

d

Out[92]:

{'key1': 'item1', 'key2': 'item2'}

In [93]:

d.keys()

Out[93]:

dict_keys(['key2', 'key1'])

In [94]:

d.items()

Out[94]:

dict_items([('key2', 'item2'), ('key1', 'item1')])

In [95]:

lst = [1,2,3]

In [96]:

lst.pop()

Out[96]:

3

In [108]:

lst

Out[108]:

[1, 2]

In [109]:

'x' in [1,2,3]

Out[109]:

False

In [110]:

'x' in ['x','y','z']

Out[110]:

True¶