We would begin with a line about Python String from the book "Pg 191, Learning Python (O'Reilly, 5e)":
Strictly speaking, Python strings are categorized as immutable sequences, meaning that the characters they contain have a left-to-right positional order and that they cannot be changed in place. In fact, strings are the first representative of the larger class of objects called sequences that we will study here. Pay special attention to the sequence operations introduced in this post, because they will work the same on other sequence types we’ll explore later, such as lists and tuples.
Table 7-1. Common string literals and operations
| Operation | Interpretation |
| S = '' | Empty string |
| S = "spam's" | Double quotes, same as single |
| S = 's\np\ta\x00m' | Escape sequences |
| S = """...multiline...""" | Triple-quoted block strings |
| S = r'\temp\spam' | Raw strings (no escapes)
print(S) # \temp\spam |
| B = b'sp\xc4m' | Byte strings in 2.6, 2.7, and 3.X
print(B) # b'sp\xc4m' |
| U = u'sp\u00c4m' | Unicode strings in 2.X and 3.3+
print(U) # spÄm |
| S1 + S2 | Concatenate |
| S * 3 | repeat |
| S[i] | Index |
| S[i:j] | slice |
| len(S) | length |
| "a %s parrot" % 'kind' | String formatting expression
print("a %s parrot" % 'kind') # a kind parrot |
| "a {0} parrot".format('kind') | String formatting method in 2.6, 2.7, and 3.X |
| S.find('pa') | String methods (see ahead for all 43): search
print('a parrot'.find('pa')) # 2 |
| S.rstrip() | remove whitespace from end
print("!" + " okay ".rstrip() + "!") # ! okay! |
| S.strip() | remove whitespace from beginning and end
print("!" + " okay ".strip() + "!") # !okay! |
| S.replace('pa', 'xx') | replacement
print("parrot".replace('pa', 'xx')) # xxrrot |
| S.split(',') | split on delimiter |
| S.isdigit() | content test |
S.lower()
S.upper() | case conversion
print("Parrot".lower()) # parrot
print("parrot".upper()) # PARROT |
| S.endswith('spam') | end test
print("is this yours".endswith("yours")) # True
print("my parrot".startswith("my")) # True |
| 'spam'.join(strlist) | delimiter join |
| S.encode('latin-1') | Unicode encoding |
| B.decode('utf8') | Unicode decoding, etc. |
| for x in S: print(x) | Iteration |
| 'spam' in S | membership |
| [c * 2 for c in S] | list comprehension to create a new list |
| map(ord, S) | map(ord, "hello") # [104, 101, 108, 108, 111]
map(lambda x: 10*x, [1,2,3,4]) # [10, 20, 30, 40] |
| re.match('sp(.*)am', line) | Pattern matching: library module |
To begin our work, we would first create a Conda environment for this using a YAML file as shown below:
Filename: string_env.yml
Note: "name: string_env" This line is where we are suggesting the name for our new environment below.
name: string_env
channels:
- conda-forge
dependencies:
- python=3.9
- pip
- nltk
- spacy
- scikit-learn
- pandas
- ipykernel
- jupyter
- jupyterlab
#-#-#-#-#-#-#-#-#-#
(base) CMD>conda env create -f string_env.yml
Collecting package metadata (repodata.json): done
Solving environment: /
Warning: 2 possible package resolutions (only showing differing packages):
- conda-forge/noarch::typer-0.3.1-py_0, conda-forge/win-64::click-8.0.0-py39hcbf5309_0
- conda-forge/noarch::click-7.1.2-pyh9f0ad1d_0, conda-forge/noarch::typer-0.3.2-pyhd8ed1abdone
Downloading and Extracting Packages
chardet-4.0.0 | 218 KB | # | 100%
pyqtchart-5.12 | 207 KB | # | 100%
parso-0.8.2 | 68 KB | # | 100%
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Preparing transaction: done
Verifying transaction: done
Executing transaction: / Enabling notebook extension jupyter-js-widgets/extension...
- Validating: ok
done
#
# To activate this environment, use
# $ conda activate string_env
# To deactivate an active environment, use
# $ conda deactivate
#-#-#-#-#-#-#-#-#-#
Suppose we are coming back after a week to work and we need to work in an environment again. What do we do now if don't remember the name?
(base) CMD>conda env list
# conda environments:
#
base * E:\programfiles\Anaconda3
pegasus E:\programfiles\Anaconda3\envs\pegasus
py39 E:\programfiles\Anaconda3\envs\py39
selenium E:\programfiles\Anaconda3\envs\selenium
string_env E:\programfiles\Anaconda3\envs\string_env
tf E:\programfiles\Anaconda3\envs\tf
#-#-#-#-#-#-#-#-#-#
(base) ~\Desktop\ws>conda activate string_env
(string_env) ~\Desktop\ws>jupyter lab
[I 2021-05-19 02:43:28.973 ServerApp] jupyterlab | extension was successfully linked.
[I 2021-05-19 02:43:29.051 ServerApp] Writing notebook server cookie secret to C:\Users\Ashish Jain\AppData\Roaming\jupyter\runtime\jupyter_cookie_secret
[W 2021-05-19 02:43:29.145 ServerApp] The 'min_open_files_limit' trait of a ServerApp instance expected an int, not the NoneType None.
[I 2021-05-19 02:43:29.191 LabApp] JupyterLab extension loaded from E:\programfiles\Anaconda3\envs\string_env\lib\site-packages\jupyterlab
[I 2021-05-19 02:43:29.191 LabApp] JupyterLab application directory is E:\programfiles\Anaconda3\envs\string_env\share\jupyter\lab
[I 2021-05-19 02:43:29.207 ServerApp] jupyterlab | extension was successfully loaded.
[I 2021-05-19 02:43:29.801 ServerApp] nbclassic | extension was successfully loaded.
[I 2021-05-19 02:43:30.176 ServerApp] Serving notebooks from local directory: ~\Desktop\ws
[I 2021-05-19 02:43:30.176 ServerApp] Jupyter Server 1.7.0 is running at:
[I 2021-05-19 02:43:30.176 ServerApp] http://localhost:8888/lab?token=57b5a01c1c12a9acab6499a55cbfcb61de9ab5e1598db126
[I 2021-05-19 02:43:30.176 ServerApp] http://127.0.0.1:8888/lab?token=57b5a01c1c12a9acab6499a55cbfcb61de9ab5e1598db126
[I 2021-05-19 02:43:30.176 ServerApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 2021-05-19 02:43:30.332 ServerApp]
To access the server, open this file in a browser:
file:///C:/Users/Ashish%20Jain/AppData/Roaming/jupyter/runtime/jpserver-1812-open.html
Or copy and paste one of these URLs:
http://localhost:8888/lab?token=57b5a01c1c12a9acab6499a55cbfcb61de9ab5e1598db126
http://127.0.0.1:8888/lab?token=57b5a01c1c12a9acab6499a55cbfcb61de9ab5e1598db126
#-#-#-#-#-#-#-#-#-#
Ques: What is the difference between "Jupyter Notebook" and "Jupyter Lab"?
Ans:
Jupyter Notebook is a web-based interactive computational environment for creating Jupyter notebook documents. It supports several languages like Python (IPython), Julia, R etc. and is largely used for data analysis, data visualization and further interactive, exploratory computing.
JupyterLab is the next-generation user interface including notebooks. It has a modular structure, where you can open several notebooks or files (e.g. HTML, Text, Markdowns etc) as tabs in the same window. It offers more of an IDE-like experience.
For a beginner I would suggest starting with Jupyter Notebook as it just consists of a filebrowser and an (notebook) editor view. It might be easier to use. If you want more features, switch to JupyterLab. JupyterLab offers much more features and an enhanced interface, which can be extended through extensions:
JupyterLab Extensions (GitHub)
#-#-#-#-#-#-#-#-#-#
Now Some Hands-On
# Picking the fifth character from a string
str_1 = "Hi, I am Ashish!"
str_1[4]
'I'
# Picking characters from fifth to tenth
str_1[4:10]
'I am A'
# Print the length of the string
print(len(str_1))
print(len(str_1[4:10]))
16
6
# Print every second character in the string
str_1[0::2]
'H,Ia sih'
# When you give negative number for indexing, it starts traversing the string from the right:
print(str_1[-1])
print(str_1[-2])
print(str_1[-5 : -1])
print(str_1[-5 :])
!
h
hish
hish!
When you are giving a range for indexing to a string, the first number should be smaller than the second, or nothing comes out:
print("str_1[-1 : -5]: ", str_1[-1 : -5], "<-")
str_1[-1 : -5]: <-
# Reverse a string
print("-->", str_1[len(str_1) : 0])
print("-->", str_1[6 : 0])
print()
"""Here it skips the first character because that's how indexing works. It excludes the last indexing number specified."""
print("-->", str_1[len(str_1) : 0 : -1])
print("-->", str_1[len(str_1) : 0 : -1])
print()
print("-->", str_1[len(str_1) : : -1])
print("-->", str_1[ : : -1])
print()
print("-->", str_1[len(str_1)+1 : : -1])
print("-->", str_1[0 : len(str_1)+1])
-->
-->
--> !hsihsA ma I ,i
--> !hsihsA ma I ,i
--> !hsihsA ma I ,iH
--> !hsihsA ma I ,iH
--> !hsihsA ma I ,iH
--> Hi, I am Ashish!
When you are specifying number for an indexing range, the number can go beyond the actual string length but not when you are picking only a character:
print("-->", str_1[len(str_1)+1])
IndexError Traceback (most recent call last)
<ipython-input-32-ae4c8bcbdc17> in <module>
---> print("-->", str_1[len(str_1)+1])
IndexError: string index out of range
# Check if a string is a palindrome
str_2 = "mom"
print(str_2 == str_2[::-1])
print(str_1 == str_1[::-1])
True
False
# Check if two string variables are actually same.
Important Note: What we are going to see in this piece of code does not hold true for lists.
v1 = str_2
v2 = str_2
v3 = 'mom'
print("v1 == v2:", v1 == v2)
print("v1 == v3:", v1 == v3)
print("v1 is v2:", v1 is v2)
print("v1 is v3:", v1 is v3)
print("id(v1)", id(v1))
print("id(v3)", id(v3))
v1 == v2: True
v1 == v3: True
v1 is v2: True
v1 is v3: True
id(v1) 2053130113968
id(v3) 2053130113968
# Now trying the same thing with lists:
animals = ['python','gopher']
more_animals = animals
print("animals == more_animals:", animals == more_animals) #=> True
print("animals is more_animals:", animals is more_animals) #=> True
even_more_animals = ['python','gopher']
print("animals == even_more_animals:", animals == even_more_animals) #=> True
print("animals is even_more_animals:", animals is even_more_animals) #=> False
print("\nMemory addresses:")
print("id(animals)", id(animals))
print("id(more_animals)", id(more_animals))
print("id(even_more_animals)", id(even_more_animals))
animals == more_animals: True
animals is more_animals: True
animals == even_more_animals: True
animals is even_more_animals: False
Memory addresses:
id(animals) 2053130940992
id(more_animals) 2053130940992
id(even_more_animals) 2053130060928
Checking what happens to a string when replace a character in a string and to a list when we replace an element in it:
owner = 'Ashish'
pets = ['python', 'gopher']
print("owner:", owner)
print("id(owner): ", id(owner))
print("id(pets): ", id(pets))
owner = owner.replace('A', 'X')
# Note: we don't have a "replace()" method for Python lists.
pets[0] = 'cat'
print("owner:", owner)
print("id(owner): ", id(owner))
print("id(pets): ", id(pets))
owner = owner.replace('X', 'A')
pets[0] = 'python'
print("owner:", owner)
print("id(owner): ", id(owner))
print("id(pets): ", id(pets))
print("Trivial replacement:")
owner = owner.replace('A', 'A')
print("owner:", owner)
print("id(owner): ", id(owner))
owner: Ashish
id(owner): 2287299151536
id(pets): 2287299204096
owner: Xshish
id(owner): 2287299080624
id(pets): 2287299204096
owner: Ashish
id(owner): 2287298874672
id(pets): 2287299204096
Trivial replacement:
owner: Ashish
id(owner): 2287298874672
Now the question is: did it actually perform the trivial replace operation in this case or not?
Creating Replace For List
# a loop to do the replacement in-place
words = ['I', 'like', 'chicken']
for i, word in enumerate(words):
if word == 'chicken':
words[i] = 'broccoli'
print(words)
['I', 'like', 'broccoli']
# a shorter option if there’s always exactly one instance:
words = ['I', 'like', 'chicken']
words[words.index('chicken')] = 'broccoli'
print(words)
['I', 'like', 'broccoli']
# a list comprehension to create a new list:
words = ['I', 'like', 'chicken']
new_words = ['broccoli' if word == 'chicken' else word for word in words]
print(new_words)
['I', 'like', 'broccoli']
# any of which can be wrapped up in a function:
words = ['I', 'like', 'chicken']
def replaced(sequence, old, new):
return (new if x == old else x for x in sequence)
new_words = list(replaced(words, 'chicken', 'broccoli'))
print(new_words)
['I', 'like', 'broccoli']
#-#-#-#-#-#-#-#-#-#
Python's in-built support for String and List
1. reversed()
>>> s1 = "Hi, I am Ashish!"
>>> ''.join(reversed(s1))
'!hsihsA ma I ,iH'
>>> reversed(s1)
<reversed object at 0x000001D587048518>
>>> list(reversed(s1))
['!', 'h', 's', 'i', 'h', 's', 'A', ' ', 'm', 'a', ' ', 'I', ' ', ',', 'i', 'H']
>>> str(reversed(s1))
'<reversed object at 0x000001D587048B70>'
>>>
>>> l1 = ['Ashish', 'Rashmi', 'Smita']
>>> reversed(l1)
<list_reverseiterator object at 0x000001D5870702B0>
>>> list(reversed(l1))
['Smita', 'Rashmi', 'Ashish']
>>>
2. sorted()
>>> sorted(s1)
[' ', ' ', ' ', '!', ',', 'A', 'H', 'I', 'a', 'h', 'h', 'i', 'i', 'm', 's', 's']
>>>
>>> sorted(l1)
['Ashish', 'Rashmi', 'Smita']
>>>
>>> l2 = ['Rashmi', 'Ashish', 'Smita']
>>> sorted(l2)
['Ashish', 'Rashmi', 'Smita']
>>>
3. len()
>>> len(s1)
16
>>> len(l1)
3
>>>
Tags: Technology,Python,Anaconda,Natural Language Processing,
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