# "Literal replace" in SymPy

## Question:

Is there a way to perform a "literal replacing" in SymPy, which matches exactly the pattern?

For example, for the expression `exp(I*theta)+exp(-I*theta)`

, I would like to replace only exp(I*t) to zero without replacing exp(-I*t)

A minimal example would be

```
from sympy import *
f=exp(I*t)+exp(-I*t)
```

Clearly, `subs`

will not work

```
f.subs((exp(I*t),0))
```

because it also replaces `exp(-I*t)`

with infinity.

## Answers:

you can use the replace method —

```
t = 2
f = exp(I * t) + exp(-I * t)
f = f.replace(exp(I * t), 0)
print(f)
```

outputs:

```
exp(-2*I)
```

hope this helps!

You can use the `xreplace`

method:

```
f.xreplace({exp(I*t):0})
```

Returns:

```
exp(-t*I)
```

Here is the documentation for reference.