In [1]:

    

import re


    

In [2]:

    

s = 'file5.txt'


    

In [3]:

    

print(re.search(r'\d+', s).group())


    

    




5

In [4]:

    

print(type(re.search(r'\d+', s).group()))


    

    




<class 'str'>

In [5]:

    

print(type(int(re.search(r'\d+', s).group())))


    

    




<class 'int'>

In [6]:

    

l = ['file10.txt', 'file1.txt', 'file5.txt']


    

In [7]:

    

print(sorted(l))


    

    




['file1.txt', 'file10.txt', 'file5.txt']

In [8]:

    

print(sorted(l, key=lambda s: int(re.search(r'\d+', s).group())))


    

    




['file1.txt', 'file5.txt', 'file10.txt']

In [9]:

    

p = re.compile(r'\d+')
print(sorted(l, key=lambda s: int(p.search(s).group())))


    

    




['file1.txt', 'file5.txt', 'file10.txt']

In [10]:

    

s = '100file5.txt'


    

In [11]:

    

print(re.search(r'\d+', s).group())


    

    




100

In [12]:

    

print(re.findall(r'\d+', s))


    

    




['100', '5']

In [13]:

    

print(re.findall(r'\d+', s)[1])


    

    




5

In [14]:

    

print(re.search(r'file(\d+)', s).groups())


    

    




('5',)

In [15]:

    

print(re.search(r'file(\d+)', s).groups()[0])


    

    




5

In [16]:

    

print(re.search(r'(\d+)\.', s).groups()[0])


    

    




5

In [17]:

    

l = ['100file10.txt', '100file1.txt', '100file5.txt']


    

In [18]:

    

print(sorted(l, key=lambda s: int(re.findall(r'\d+', s)[1])))


    

    




['100file1.txt', '100file5.txt', '100file10.txt']

In [19]:

    

print(sorted(l, key=lambda s: int(re.search(r'file(\d+)', s).groups()[0])))


    

    




['100file1.txt', '100file5.txt', '100file10.txt']

In [20]:

    

print(sorted(l, key=lambda s: int(re.search(r'(\d+)\.', s).groups()[0])))


    

    




['100file1.txt', '100file5.txt', '100file10.txt']

In [21]:

    

p = re.compile(r'file(\d+)')
print(sorted(l, key=lambda s: int(p.search(s).groups()[0])))


    

    




['100file1.txt', '100file5.txt', '100file10.txt']

In [22]:

    

l = ['file10.txt', 'file1.txt', 'file5.txt', 'file.txt']


    

In [23]:

    

# print(sorted(l, key=lambda s:int(re.search(r'\d+', s).group())))
# AttributeError: 'NoneType' object has no attribute 'group'


    

In [24]:

    

def extract_num(s, p, ret=0):
    search = p.search(s)
    if search:
        return int(search.groups()[0])
    else:
        return ret


    

In [25]:

    

p = re.compile(r'(\d+)')


    

In [26]:

    

print(extract_num('file10.txt', p))


    

    




10

In [27]:

    

print(extract_num('file.txt', p))


    

    




0

In [28]:

    

print(extract_num('file.txt', p, 100))


    

    




100

In [29]:

    

print(sorted(l, key=lambda s: extract_num(s, p)))


    

    




['file.txt', 'file1.txt', 'file5.txt', 'file10.txt']

In [30]:

    

print(sorted(l, key=lambda s: extract_num(s, p, float('inf'))))


    

    




['file1.txt', 'file5.txt', 'file10.txt', 'file.txt']

In [31]:

    

l = ['100file10.txt', '100file1.txt', '100file5.txt', '100file.txt']


    

In [32]:

    

p = re.compile(r'file(\d+)')
print(sorted(l, key=lambda s: extract_num(s, p)))


    

    




['100file.txt', '100file1.txt', '100file5.txt', '100file10.txt']

In [33]:

    

print(sorted(l, key=lambda s: extract_num(s, p, float('inf'))))


    

    




['100file1.txt', '100file5.txt', '100file10.txt', '100file.txt']