7b: handling text - string and files

Maybe some of you have already used this one: this turns the string to lowercase.

Is this a fruitful or void method?

s = "This string was written in Amsterdam"

var1 = s.lower()

print(s.lower())
print(var1)

the opposite is upper()

s = "This string was written in Amsterdam"

print(s.upper())

.strip(): by default, it will remove spaces, tabs, line breaks and other ‘space-like’ characters from begin and end of the string. You can also indicate wich characters you would like to strip.

var1 = "how are you?"

print("hi all %s" % var1)

s = "   this sentence contains some space at the beginning and the end   "

#s = s.strip()

print("|%s|" % s)

s = "*-* this string starts with *-* and ends with *-*?"

# You can just list all the characters that you do not want to have at the beginning or end of the string
print(s.strip("*?!- "))

.replace(<old, <new>). Replace all occurrences of <old> with <new>

.replace(<old>, <new>, <max>). Replace <max> times <old> with <new>

s = "the United States is losing its democracy"

news = s.replace("losing", "fighting for")

print(news)

You can also use this to remove characters. (In contrast to strip, this works across the entire string).

s = "I just can't stand the letter t"

s2 = s.replace("letter","")
print(s2)

You can indicate how many occurences you wan to replace:

s = "I just can't stand the letter t"

s2 = s.replace("t","",2)
print(s2)

Some of you know that you can turn a string into a list of it's characters:

lst = list("this will be a list")
print(lst)

With split.(<delimiter>) you can split a <string> at every occurrence of any <delimiter> into a list of substrings!

It leaves out the delimiter which is by default a space.

s = "this will be a list"
print(s.split())
print(s.split(" "))
print(s.split("be"))

s = """Sometimes you want to cut up a string in a different way.
For example if it contains several sentences. Then you
could for example split it using the period closing a sentence.
"""

lst = s.split(".")

lst2 = []
for i in lst:
    lst2.append(i.replace("\n",""))
print(lst2)

the \n sign is the way Python stores a "newline" (an "enter").

It is possible to write a number like a string (just like you can write it as a float or an integer).

With isnumeric you can check if a string is a number:

s = "100"

print(s.isnumeric())

When a limited number of statements requires a file to be open, it is elegant to do the file handling in a separate block of code. This construction implies automatic closing of the file after the block is executed.

This is the syntax:

with open(<file path>, <mode>) as finput:
   <statement>
   ...
   <statement>

If only a name is specified, Python will assume that the file is in the current/same directory where the Python file is saved and executed. You can also add the full path if the text files is saved in another location than the Python file.

You can open a file in different modes, the most common are:

• "r", reading (no change to the file will be done)
• "w", writing (content will be written into the file, it is usually used when an output file is created)
• "a", appending (start writting at the end of this file.)

By default, if we open a file and do NOT specify the mode, it will do it in the 'reading' mode.

After you have opened the file as <file>, you cannot directly work with that object.

Two often-used methods to work with the file are .read() and .readlines().

• .read() outputs the entire file (as a string)
• .readlines() outputs a list in which every item represents a line (as a string)

with open("example.txt") as file:
    output1 = file.readlines()

var1 = "lalalalalal"
# output is now a list of strings
for line in output1:
    print("%s %s" % (line,var1))
    print("----")

What happens here?

1. I open the text file as "file".
2. "file" is an object that we cannot use directly. We still have to unpack it.
3. I use the method ".readlines() to unpack the file as a list of lines (as strings).
4. I then save that list in a new variable.
5. That new variable is available outside of the with-block (while the "file"-object is closed (and therefore unavailable) outside the code block.)

I can also use the method .read()

Then the file is unpacked as one string.

with open("example.txt","r") as file:
    output = file.read()

for i in output:
    print(i)