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f22/meena_lec_notes/lec-27/.ipynb_checkpoints/files_and_directories-checkpoint.ipynb deleted 100644 → 0
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%% Cell type:markdown id: tags:
# Files and directories
%% Cell type:code id: tags:
``` python
from IPython.core.display import display, HTML
display(HTML("<style>.container { width:100% !important; }</style>"))
```
%% Cell type:code id: tags:
``` python
# import statements
import os
```
%% Cell type:markdown id: tags:
### Review 1: What does sorted() return?
%% Cell type:code id: tags:
``` python
d = {"Andy": [850, 955], "Meena": [1100, 1320], "Peyman": ["online"]}
t = (45, 32, 29)
sentence = "Meet me at the Sett"
my_list = sentence.split(" ")
# Uncomment each line and observe the types
#print(type(sorted(d)))
#print(type(sorted(t)))
#print(type(sorted(sentence)))
#print(type(sorted(my_list)))
```
%% Cell type:markdown id: tags:
### Review 2: Does sorted return a new object instance or modify the existing object instance?
%% Cell type:code id: tags:
``` python
# sorted returns a brand new object instance, whereas sort() method modifies the existing object instance
```
%% Cell type:markdown id: tags:
### Review 3: Difference between + and append() method on lists
%% Cell type:code id: tags:
``` python
listA = ["Wisconsin", "Madison"]
listB = ["Data" , "Science"]
#print(listA + listB) # + operator creates a brand new object instance
#print(listA[1] + listB[1]) # just like + operator on strings creates a brand new string object instance
# recall that strings are immutable, so you don't have a choice there
#listA.append(listB) # append() method modifies the existing list object instance
#print(listA)
```
%% Cell type:markdown id: tags:
## File processing
- open(...) function call
- file_object.close() function call
%% Cell type:markdown id: tags:
## Reading data from a file
- using read() function call:
- returns file contents as one big string
- convert file object into a list
- each line becomes an item within the list
- works because file objects are iterators
- using for loop to iterate over every line
- works because file objects are iterators
- using next(...) function call to extract a single line
- useful when you want to just process the initial few lines of a file
- ex: extract header line alone from a csv file
%% Cell type:markdown id: tags:
Using read() function call ...
%% Cell type:code id: tags:
``` python
sample_file = open("sample_file.txt")
data = sample_file.read()
sample_file.close()
data
```
%% Cell type:markdown id: tags:
What is the type of return value of read() function?
%% Cell type:code id: tags:
``` python
type(data)
```
%% Cell type:markdown id: tags:
Converting file objects into a list
%% Cell type:code id: tags:
``` python
sample_file = open("sample_file.txt")
data_list = list(sample_file)
sample_file.close()
data_list
```
%% Cell type:markdown id: tags:
What is the type of data_list?
%% Cell type:code id: tags:
``` python
type(data_list)
```
%% Cell type:markdown id: tags:
Using for loop to iterate over file object
%% Cell type:code id: tags:
``` python
sample_file = open("sample_file.txt")
for line in sample_file:
print(line)
print(type(line))
sample_file.close()
data_list
```
%% Cell type:markdown id: tags:
Using next(...) to extract just first item (first line) from file objects
%% Cell type:code id: tags:
``` python
sample_file = open("sample_file.txt")
one_line = next(sample_file)
print(one_line)
print(type(one_line))
sample_file.close()
data_list
```
%% Cell type:markdown id: tags:
### Writing data into a file
- "w" mode in open(...) function call
- BE CAREFUL: every time you invoke open, you will overwrite the file's contents
%% Cell type:code id: tags:
``` python
hello_file = open("hello.txt", "w")
hello_file.write("Hello CS220 / CS319 students.\n")
hello_file.write("Good luck with exam 2 preparation.")
hello_file.write("Ooops forgot newline")
hello_file.close()
```
%% Cell type:markdown id: tags:
Let's read the contents from the file we just wrote
%% Cell type:code id: tags:
``` python
hello_file = open("hello.txt")
data = hello_file.read()
hello_file.close()
data
```
%% Cell type:markdown id: tags:
## os module functions
- os.listdir
- os.mkdir
- os.path.exists
- os.path.isfile
- os.path.isdir
- os.path.join
%% Cell type:code id: tags:
``` python
os.listdir(".")
```
%% Cell type:code id: tags:
``` python
os.mkdir("test_dir")
```
%% Cell type:code id: tags:
``` python
# os.path is a sub-module of os --- does not need importing again
print(os.path.exists("some_file.txt")) #does this file (at this path) exist?
print(os.path.isfile("test_dir")) #nope
print(os.path.isdir("test_dir")) # yes
```
%% Cell type:markdown id: tags:
### os.path.join is a very important function, which enables portability of code
- portability enables you to write code in one OS platform and run it on another OS platform
%% Cell type:code id: tags:
``` python
# this function is like the regular join method, which combines things into a string
# but automatically senses which OS you are using and joins them with either a \ or /
path = os.path.join("test_dir", "file1.txt")
print(path)
# what do you get?
```
%% Cell type:markdown id: tags:
## Exception handling
%% Cell type:code id: tags:
``` python
# let's figure out how to handle a command to open a file that does not exist
path = input("enter the name of the file to open:")
try:
file_object = open(path, "r") # "r" is for reading, but is the default
d = file_object.read()
print(d)
file_object.close()
except FileNotFoundError as e:
print(type(e))
print(path, "could not be opened")
```
%% Cell type:markdown id: tags:
### Python is all about shortening code. Is there a way to shorten the process of:
- opening a file
- handling any Errors while reading/writing
- closing the file
%% Cell type:code id: tags:
``` python
# we can use a 'with' statement to shorten our code
import random
with open("some_numbers.txt", "w") as f:
for i in range(10):
f.write(str(random.randint(1,100)) + "\n")
# don't need to close
# don't need to worry about try/except
```
%% Cell type:markdown id: tags:
### Sum example
%% Cell type:code id: tags:
``` python
#Solution 1: bad solution because we do a lot of reading work before we do any addition (miss the bug)
f = open("nums.txt")
nums = list(f)
f.close()
total = 0
for num in nums:
total += num
print(total)
```
%% Cell type:code id: tags:
``` python
#Solution 2: better solution because start adding immediately after reading numbers from each line
#(catch bugs quickly)
f = open("nums.txt")
total = 0
for num in f:
total += num
print(total)
f.close()
```
%% Cell type:code id: tags:
``` python
#Solution 2: with fix for the bug
f = open("nums.txt")
total = 0
for num in f:
total += int(num)
print(total)
f.close()
```
%% Cell type:markdown id: tags:
### Recursive file search
%% Cell type:code id: tags:
``` python
# program recursive file searcher
import os
def recursiveDirSearch(searchDirectory, searchFileName):
for curr in os.listdir(searchDirectory):
# build a path to this current thing
curr = os.path.join(searchDirectory, curr)
#check if curr is a file
if os.path.isfile(curr):
#check if it contains the search name
if searchFileName in curr: # base case...no recursive call
f = open(curr)
contents = f.read(50) # reads first 50 chars into a string
f.close()
return contents
else: # recursive case!!
contents = recursiveDirSearch(curr, searchFileName)
if contents != None: # we found something
return contents
# finished all recursive searching and never found it
return None
# this function is like our main program
def dir_search(dir_name, file_name):
if not os.path.exists(dir_name):
print("Unable to find searchDirectory!")
else:
contents = recursiveDirSearch(dir_name, file_name)
if contents != None:
print(contents, end = "")
# TODO: figure out how to print "<file_name> not found"
```
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{"meena": 20, "viyan": 30, "rogers":40}
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{'meena': 20, 'viyan': 30, 'rogers':40}
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{"meena": 20, "viyan": 30, "rogers":40,}
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{"meena": false, "viyan": true, "rogers":false}
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{"meena": False, "viyan": True, "rogers":False}
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{"meena": None, 10: 20, "rogers":10}
f22/meena_lec_notes/lec-27/cs220_survey_data.csv
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Hello CS220 / CS319 students :)
Hope you are having a wonderful day!
f22/meena_lec_notes/lec-27/lec_27_pandas1.ipynb
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hi
\ No newline at end of file
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